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How to Pick the Right Battery Charger

Choosing a Battery Charger

Let me start with a disclaimer: does not sell inexpensive, off-the-shelf chargers often found at retail outlets and certain other online stores. We cater specifically to microprocessor-controlled chargers, also known as smart chargers. All the chargers we stock are reviewed, tested and selected based on function, reliability and durability. These chargers are designed to charge lead acid and other types of batteries based on computer-generated algorithms. Simply put, the charger collects information from the battery and adjusts the charge current and voltage based on this information. This allows the battery to be charged quickly, correctly, and completely when using a smart charger. All the chargers we sell can remain connected to a battery indefinitely and will not overcharge or damage it.

Here are some simple steps to select the right charger for your needs.

Step 1: Choosing a Charger Based on Battery Type

Whether your battery is maintenance free, wet cell (flooded), AGM (absorbed glass mat), gel cell or VRLA (valve-regulated lead acid), one charger should work for all types except for gel cell. However, some of our gel cell chargers will work well with the other battery types.

Step 2: Determining Battery Size

Selecting a Battery Charger

We don’t mean physical size, but how many amp hours your battery stores. For example, a typical full-size auto battery is about 50 amp hours, so you would choose a 10 amp charger that would take about 6 hours to recharge it if the battery were completely dead. Another instance would be a marine deep cycle battery rated at 100 amp hours. It would take a 10 amp charger about 11 hours to recharge a dead battery to near 100% full charge. To calculate your total charge time, a good rule of thumb is to take the amp hour rating of the battery and divide by the charger rating (amps) and then add about 10% for the extra time to totally top off the battery.

Some folks wanting quick recharge should look for a charger with more amps. If you’re not in a hurry, you can select a smaller charger. The most important thing is to make sure you have enough charger power to do the job you require in the time you allocate.

Step 3: Choosing a Battery Charger Based on Desired Outcome

Buying the Right Battery Charger

Some folks require a charger to keep their motorcycle, classic car, or aircraft battery charged during the off season. In these cases, a simple low current charger will work fine. Others require a fast and powerful charger to quickly restore a trolling motor battery or a wheel chair battery set. Other types of chargers and the reasons you might need them:

  • MULTI VOLTAGE Input chargers for use when visiting a foreign country
  • Waterproof chargers for those times when you’re out in the elements
  • Chargers that double as power supplies for RV use
  • Multi-bank chargers for charging multiple batteries simultaneously

Hopefully, we’ve helped you figure out which is the best charger for your application. Additional questions? Let us know in the comments below.

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  • I have a AGM battery that was originally used on a solar sysytem. I have a Schumacher charger that has a setting for this type battery. The other day I went to charge it and it was very low 9% according to the charger. It charged fairly quickly to about 62% then plateaued off. I noticed that the wires next to the clamps got very hot. Any thoughts? My goal is to take this battery with me camping and use it with my CPAP machine. I dont have it in front of me but its 12 Volt. About the size of a large car battery.


    June 24, 2016 a 7:03 am
    • Charging cables heating up could be the result of a couple of factors. Heat is a sign of resistance, which means the current coming from the charger isn’t being accepted somewhere along the line. If the battery is also heating up that could elude to a bad battery not being able to accept the charge, and it might be time to replace the battery. If the battery is not heating up, but the wire at the connection point is, i would try cleaning the terminals and ensuring you have a good connection.

      BatteryStuff Tech
      January 18, 2017 a 11:49 am
    • An excellent and very informative article, thank you!

      I have a newer sealed, maintenance free, mid-range (in terms of quality) standard AGM 12v deep-cycle Marine/RV battery

      930 marine cranking amps, 145 minutes reserve capacity, 75 amp-hours.

      This is my first experience with AGM batteries of any sort.

      My question: Is the electrolyte, absorbed into the glass matting, in these AGM batteries subject to stratification in the same way that the electrolyte in a flooded wet battery is?

      Reason I ask: I use a smart charger that incorporates 8 steps in the charging/maintenance cycle. The 1st step is an automatic desulfation step. The 6th step is an OPTIONAL step that can be used occasionally to “recondition” or destratify the electrolyte in flooded wet batteries. This is accomplished by the application of 15.8v, for short periods of time depending on the voltage of the battery, to induce out-gassing and turbulence due to the rising bubbles. Destratification occurs when the turbulence causes the electrolyte to be mixed and rendering the SG uniform throughout the depth of the cell.

      My obvious next question: Will it ever be necessary, or even safe, to use this optional 6th “reconditioning” step when charging/maintaining this mid-range, deep-cycle AGM battery?

      June 22, 2016 a 7:48 am
      • AGM Batteries have the electrolyte absorbed into the fiberglass matting so stratification is not a concern with these batteries, such in wet cells where the acid can separate from the water. The other main reason to equalize a battery is to cause the sulfation to dissolve back into the electroylte, however not all AGM battery manufacturers recommend this processes, as some AGM batteries are not meant to withstand this type of charge. The process of equalizing a battery causes the battery to heat up and gas. While the gassing can work itself out of the battery vents, some manufacturers do not have large inner cell connectors to withstand that type of charge. Lifeline Battery is one of the manufacturers we carry that does promote equalizing their batteries. In the end you need to contact the manufacturer of your battery to see what they recommend.

        BatteryStuff Tech
        January 18, 2017 a 8:11 am
      • Hi there.
        I’m doing a summer project and was wondering about deep cycle batteries.
        I understand that when connecting the same batteries in parallel, it will have the same voltage but will double up in the Ah. However, let’s say I am charging the battery in parallel.
        Let’s assume that the rating max charging current for a battery is 5 Amps and I have an 8 Amp charger. Would connecting the battery in parallel be able to handle 8 Amp charger? (Meaning that the rating max charge current will be 10 amps instead of 5 amps?? Or would the max rating current to charge is still 5 amps and can not handle it. I was wondering about this because wouldn’t that mean the battery will charge slower if it only takes in 5 amps? I guess it might be better for the battery life but was wondering if it could handle it)

        Thanks for your help.

        June 28, 2016 a 11:29 pm
        • Please keep in mind we only recommend interconnecting batteries that are of the same age, capacity, chemistry, and if you plan to employ them as a battery pack. We however do not recommend connecting batteries together that you are not going to employ as a battery pack. The answer to your questions is yes, assuming these are lead acid batteries. If a single battery has a max amp rating of 5 amps, and you put that battery in parallel to increase the amp/hr, then the max rate is thereby increased, so it would now be 10 amps. The reason this works is the charge is spread out among both batteries, and not just one.

          BatteryStuff Tech
          January 19, 2017 a 10:10 am
        • I’m planning to purchase a 12v 35amp hour AGM battery for use with a cpap machine while camping. We have also selected a 400w continuous use/800w peak power inverter to use. I’m having a hard time knowing what type of charger to purchase, as I’m on a tight budget. I know you have higher quality chargers listed, which is great, but I don’t know what type of charger I can use at all. A lot of the reviews mention float chargers, which works for storage – but I need something that will ensure the machine is able to run at night, and can be charged via wall socket during the day. Would a 2/6amp, 6/12v manual charger with self-resetting circuit breaker and an automatic trickle charger after the battery is full work for this?

          For reference this is what the CPAP machine says under the electrical version of the manual, and this is where I get a little confused (though I have had others tell me they use this battery and inverter with their cpap just fine – but they use a 3 panel 45 watt solar charger which is unfortunately out of my price range.):
          AC power consumption (with 60w power supply) 100-240 VAC, 50/60 Hz, 2.1 A
          Ac Power consumption (with 80w power supply) 100-240 VAC, 50/60 Hz, 2.0 A
          DC Power consumption: 12 VDC, 6.67 A

          Any help or explanations are appreciated, as I am brand new to trying to figure this stuff out. :)

          July 4, 2016 a 9:56 am
          • We get this question quite a bit, so don’t worry about being confused! The first thing you need to figure out is how your going to run a CPAP machine off a battery. Are you going to use the inverter? Using an inverter is not my first choice as they draw more out of the battery, than going straight off the battery. If you look at your 3rd power rating it tells you the CPAP Machine can run directly off a battery with a rating of 12VDC, which is a 12 volt battery, and it will pull 6.67 Amps an hour. Now you may think that is more amperage than using the inverter, which draws 100-240VAC @ 2.1 Amps. However, when you calculate that back to the battery it is pulling 23.18 Amps an hour! So going off the battery is a better choice! You will most likely have to contact the CPAP manufacturer for a 12v accessory meant to run the machine directly off the battery, but it is far more efficient.

            Next, either way your 35 AH rated battery would not work, as you don’t want to discharge your battery more than 50%. My suggestion would be to use two calculators to first select your correct battery. First if your going to use the inverter you will need the Calculator | DC to AC amperage conversion run through an Inverter to obtain your DC Amp Draw. Then plug the DC amp draw into the Calculator | Sizing a 12 Volt Battery to a Load to figure out what AH rated battery you need based off how many hours you plan to sleep. And, finally in order to answer your question about charging… You can select a smart charger that has an amp rating of up to 25% of the batteries AH rating. So if you end up with a 100AH rated battery you can use a 25 Amp Charger. Charging any faster could hurt the battery, and we only recommend smart chargers for charging.

            BatteryStuff Tech
            January 25, 2017 a 8:26 am
          • Excellent advice & removal of some of the mystery of how to pick the proper charger, and terms used.


            March 5, 2012 a 3:55 am
            • I had never seen this on your page before, well done!

              April 20, 2012 a 5:52 am
              • excellent website to know more about picking up battery charger,thanks.

                April 20, 2012 a 1:09 pm

                  ARTHUR SIMON
                  July 7, 2012 a 12:44 pm
                  • Not every smart charger will have the “voltage ramp up”. Those that do, such as the Soneil or Noco genius, the voltage spike is the first thing it does, to quickly remove fresh sulfation. This high voltage to a discharged battery will not overcharge it. Once the battery is full, it will keep and miantain it. The voltage will not spike to 15 or 16 volts when the battery should be kept at 13.2.

                    Other chargers, such as Pulse Tech or Battery MINDer removes sulfation with high frequency pulses, not voltage pulses. This is safe, harmless, and effective in restoring battery life when used regularly.

                    BatteryStuff Tech
                    July 9, 2012 a 9:40 am
                  • I can recommend the La Crosse Technology BC-700 charger.

                    This is a pretty sophisticated battery charger. I‘ve always just had simple ones but this one does far more. I‘m not even sure I understand all the functions and I‘m fairly techno-geeky.

                    More info:

                    Brendan Kiely
                    July 19, 2012 a 12:30 am
                    • Yes, it looks like a very nice NiMH and NiCD battery charger. Thanks for sharing.

                      BatteryStuff Tech
                      July 19, 2012 a 8:30 am
                    • Super Informative. You saved me from ruining my batteries!!! Hat‘s Off To You!!!

                      August 24, 2012 a 10:30 pm
                      • I have a question. I have a 15 foot bass boat,first boat ever and do not know a lot about the difference in batteries and all I know is it looks like a sealed car battery. I do not have any idea which charger I should get ,would sure like to know so I get the right one

                        September 11, 2012 a 10:34 am
                        • Is there any information on the battery at all? If so, please provide it and I can help determine what you need.

                          BatteryStuff Tech
                          September 11, 2012 a 11:05 am
                        • I currently have a 24V set-up in my bass boat for the trolling motor. I upgraded to Optima Blue top batteries a few months ago. I installed a new 3-bank, 10amp DualPro charger the same day I installed the new batteries. I fully charged the batteries before using the boat. About two weeks later we fished a 3-day tournament and promptly wore out two new, fully charged Optima batteries in 7-8 hours of fishing each day. Yes, I charged them all night before the first fishing day. My partner lays on the trolling motor well more than I do: however, killing the batteries wasn‘t really the issue. Well, other than listening to him gripe about it and how HIS Skeeter‘s 36V TM system lasts all day and THEN SOME.

                          Anyway – I plugged in between 4pm-6pm on day #1 day (at our lodging on normal electricity) to charge the batteries. By 5am THE NEXT MORNING…the batteries were STILL NOT FULLY CHARGED. Same thing happened on morning #2 and #3. The starting battery was was obviously fully charged each day; however, depending on the TM battery, one may have been about 90% charged; the other in it‘s final stage (like 98%). The next day one TM battery was like 80% and the other 90%…after 12 hours on the juice. Brand new batteries on a brand new charger. I don‘t get it!!

                          Optima “recommends” using 10A chargers on their blue top batteries (if not all their batteries). I‘m considering moving to a 36V trolling motor. Here‘s my question. I‘m going to have to upgrade to a 4-bank charger to do this. I don‘t want to trash two Optima batteries that I just bought. I also don‘t want to wait 12-hours to have fully charged batteries. The charger I want to go to chargers at 30A, and I don‘t think it has a regulator (Protournament 300 Quad). That said, will 30A charger HURT the Optima batteries?

                          10A is going to take 10-12 hours to recharge a depleted trolling motor battery…no biggie for non-tournament fishing…but when you need the boat ready to go 12 hours after you get out of it…12 hours to charge two 12V batteries ain‘t cutting it. Had I known it was going to take 12-hours to get a full charge I wouldn‘t have bought the Optima batteries. To hear my partner tell it, his Odyessy batteries are FAR SUPERIOR to Optima anyway.

                          September 18, 2012 a 11:21 am
                          • What are the AH (Amp Hours) ratings on the Optima batteries? This will determine what I recommend as far as good charge rate goes. 10%-35% of the battery capacity is safe range to charge with. Also, what is the draw amount of the trolling motor? Maybe your batteries don‘t have the capacity to handle the motor for as long as you thought. At least, that‘s one possibility. Is your current 10 amp Dual Pro charger 10 amps per bank? Or 10 amps total of all three banks?

                            BatteryStuff Tech
                            September 20, 2012 a 9:10 am
                          • Hello. I have a basic folding camper. The units were never factory fitted with electrics let alone a charging system. Which may well be a good thing as the most popular UK charging units fitted to caravans, campers and trailer tents only charges at 13.6V. So not only does it take an age to charge it never fully charges. My choice previously has just been to use a “dumb” charger. You sell intelligent chargers, now until recently I‘d never seen intelligent chargers with high single digit AH rates let alone double digit AH rates. Now I may well use a low rated intelligent charger to keep my battery conditioned when at home but what about on site? If I‘m on an EHU (Electric Hook Up not sure American term) I‘m not charging and running the battery in separate cycles. A whole range appliances may be plugged in whilst charging the battery. Does the use of appliances confuse the charger? How does it asses the battery if at the same time resistive loads, inductive loads or both are being taken out. The batteries used tend to be 80AH or 100AH “pseudo” leisure batteries. I say pseudo leisure batteries because there is some debate in the UK on how much thicker the plates are on these starter sized batteries as against the full thickness in 2V cells. Simple lead acid batteries or glass mat are generally used. The demands light (ish) lighting, audio, limited TV, water pump. To be honest as demand is low and temp reasonable battery life is quite good. More a case of being curious how intelligent chargers work if you‘re taking load at the same time? Thanks In Anticipation.
                            October 4, 2012 a 4:26 am
                            • With smart chargers, if they are on and charging and they ‘sense’ a load applied to the batteries, they will automatically attempt to supply the load so the batteries will not be discharged. Most chargers are not rated to handle a full load and they can burn out. However, we have chargers that are also power supplies (converters).

                              Iota, Power Max, and Samlex are the brands of chargers that we carry with this capability. They can charge the batteries and at the same time supply a load to your applications up to the rated charge rate of the charger (in amps). For instance, a 12 volt 30 amp charger can supply a load up to 30 amps. If the load is higher, at that point the batteries will be used for the remainder.

                              BatteryStuff Tech
                              October 4, 2012 a 8:36 am
                            • I lost the charger P/N 700150 for a Craftsman cordless hedge trimmer 24 VDC model 240.74802 I am looking for a replacement charger. Thanks

                              October 12, 2012 a 5:03 am
                              • That part number isn‘t one that we carry. Sorry. Is the charger for a NiCD battery? Lead Acid? Lithium?

                                BatteryStuff Tech
                                October 12, 2012 a 9:16 am
                                • Have you located a place that does carry this charger, as I have a enew trimmer, Model number 240.74802, need a charger.

                                  July 31, 2014 a 9:19 am
                              • I just purchased a new V Star Custom 650. The manual says it has a Valve Regulated Lead Acid Battery. It says not to use a Conventional Battery Charger. I have a Yuasa 1.5 Amp 5 Stage Battery Charger. It says to use it on conventional batteries and maintenance-free AGM batteries. What do I use for this bike????? Now I have to buy another charger? Thank you very much for your help.

                                Allen Dorak
                                October 20, 2012 a 4:20 pm
                                • Your Yuasa smart charger should be just fine for your VRLA battery. VRLA batteries are technically wet batteries, but they are sealed with an internal drip system to prevent the water from evaporating and leaving the cells. The electrolyte is not absorbed in a glass matte like an AGM.

                                  BatteryStuff Tech
                                  October 23, 2012 a 10:26 am
                                • I live full time in a 1977 GMC motorhome. Three batteries/bank: 1 red top, 1 yellow top, and 2 6v golf cart. Red for the engine; yellow for the 6K genset (Onan); golf carts for the house. Solenoids separate all three until the ignition is on.
                                  Converter, 40 amp, has never fully charged the three units with the ignition on; nor even the house and genset batteries with the ignition off. Now the converter is not operating. I need a converter/charger that will do the job through perhaps a change in wiring?

                                  Don Eddy
                                  November 13, 2012 a 12:06 pm
                                  • Are you looking for a single bank charger/converter, or multi-bank?

                                    BatteryStuff Tech
                                    November 13, 2012 a 12:44 pm
                                  • Cool article, saved me a lot of time.
                                    But I‘m not sure if I understood everything right, so I‘ll need some guidance.
                                    I have a electric van, batteries: 18 in series per row, 3 of those rows in parallel, mounting to 54 batteries. They are AGM 12v 100Ah.
                                    What type of charger and how many of them do I need?

                                    November 13, 2012 a 1:58 pm
                                    • What is your total system voltage? 72 volts? Then I recommend a 72 volt charger for the entire thing configuration. With 300 AH, I recommend a 30 Amp charger. However, the closest we carry is an Eagle 72v 12 amp charger.

                                      BatteryStuff Tech
                                      November 13, 2012 a 4:19 pm
                                    • My battery charger (HP-1202B 24V2A) for my Phantom wheel chair does not work any more (I think it overheated). HP no longer makes this battery charger, so I ordered one from another supplier, but it did not work (though it had the above specifications). From where can I obtain one, and how do I know it will work. Thanks, Patrick

                                      December 5, 2012 a 2:16 pm
                                      • We do not sell HP chargers. I do not know where you can find one.

                                        What are the types of batteries your wheelchair uses? Lithium, NiCD, Sealed Lead Acid?

                                        BatteryStuff Tech
                                        December 5, 2012 a 4:07 pm
                                      • Can I use a standard (1-stage) charger, set on 2amps to charge my new AGM 12AH motorcyle battery for initial use until I get a smart charger? Also, is an AGM battery also a VRLA battery? The box the battery came in called it AGM but the instructions that came w/battery call it a VRLA??? It has the multi-bottles of acid that you put in and seal. I appreciate any info.

                                        December 15, 2012 a 7:33 am
                                        • You may use a 1 stage charger, but watch it carefully to you don‘t over charge your new battery. If your AGM battery came with an acid pack, it requires activation. But once the cells are sealed with the cap strip, there is no need to ever open it up again. Valve Regulated Lead Acid is often associated with AGM batteries.

                                          BatteryStuff Tech
                                          December 17, 2012 a 8:39 am
                                        • I recently purchased a Schumacher SSC-1000a smart charger for my new AGM marine battery. I have monitored the charging cycle and see no evidence of a 3 step process whereby the regulated voltage is dropped back as the battery approaches full charge. I have monitored this voltage with my digital meter and the digital voltage reading on the charger itself and have noticed the regulated voltage increases more as the battery approaches full charge. On the 10 amp rate the regulated voltage is just over 16 volts near full charge. And on the 6 amp rate the regulated voltage is just under 16 volts near full charge. This happens the same on the standard setting with a lead acid battery.

                                          Is my charger working properly? Or is it not really a smart charger?

                                          December 27, 2012 a 7:46 am
                                          • 16 volts sounds like it‘s too high, even for high performance AGM batteries. The charger is suppose to be automatic, but it may be defective.

                                            BatteryStuff Tech
                                            December 28, 2012 a 8:59 am
                                          • which charger would be used on a polaris sportsman 500 2008

                                            December 29, 2012 a 1:35 pm
                                            • Pretty much any of our motorcycle chargers will work. Battery Tender is the most popular brand, but I personally recommend Pulse Tech. Please take a look at our 12 volt battery chargers. Anything 4 amps and under will work for you.

                                              BatteryStuff Tech
                                              January 2, 2013 a 8:33 am
                                            • Great article! could you please help me out. i am making a go kart, planning to connect 4 12v 80Ah VRLA batteries in series. what kind of charger should i use?

                                              January 8, 2013 a 9:42 am
                                              • I recommend a 48 volt charger, of course. Anywhere from 4 – 16 amps of charge rate should be fine. 8 amps would be my recommendation. Just make sure the charger is compatible with VRLA batteries (AGM if they are sealed batteries).

                                                BatteryStuff Tech
                                                January 8, 2013 a 10:01 am
                                                • I was just wondering – theoretically would using 2 24v chargers or 4 12v chargers simaltaneously be better than a single 48v charger(besides the cost)?

                                                  January 10, 2013 a 6:35 am
                                                  • If your 48 volt system is used as a single unit, it‘s best to charge it altogether the same way. However, you can charge the batteries independently using multi-bank chargers, or separate chargers. Just make sure your connects are correct. You can‘t stack two chargers on a single battery.

                                                    BatteryStuff Tech
                                                    January 10, 2013 a 8:56 am
                                                    • i just read somewhere and was confused if the charger is to be connected to the battery directly or does the controller have any role to play in the charging process?

                                                      January 23, 2013 a 8:52 am
                                                      • Controllers are recommended for solar chargers. But standard AC plug-in chargers are micro processor controlled, there is no need for any additional controlling. Hookup directly to the battery is the best method of charging.

                                                        BatteryStuff Tech
                                                        January 23, 2013 a 9:08 am
                                              • Very Informative page….I have a question regarding charge/absorption on a 24 volt battery bank. What is the highest voltage that should be used to charge a 230 AH/24 volt bank. I have been told a 48 volt charger can be used safely but sounds a bit suspecious to me….

                                                January 24, 2013 a 5:50 am
                                                • 48 volts will not charge a 24 volt system ‘faster’. It will cause harm. My suggestion is that ~29.6 volts is the highest voltage rate I recommend for a 24 volt system. Now, amps is a completely other story. I advise that 25% of your capacity should be the max charge rate you should use. We recommend 10% unless you need the quickest charge time.

                                                  BatteryStuff Tech
                                                  January 24, 2013 a 9:11 am
                                                • Love your site and your service. One question I have… I just purchased a Motocross YTZ14S from you folks for my Honda VFR800. I believe that the battery I received was an AGM, but I‘m not sure. Its not listed anywhere on the battery itself, nor is it on the invoice. I‘m using a Noco G1100 to keep it charged. As I‘m sure you know, The G1100 can run in Normal mode, or Cold/AGM mode. Will it harm it to use the Normal mode for charging or do I have to use the AGM mode? The manual for the charger says that if your unsure of the battery makeup, use the Normal mode. What does the charger do differently in AGM mode? Thanks for any light you can shed on this.

                                                  February 4, 2013 a 6:05 pm
                                                  • The YTZ14S from Motocross is an AGM battery. However, it is not on the same level as high performance AGM batteries, such as Odyssey or Optima. These AGM batteries actually recommend charging at a higher voltage than what is considered normal, or safe for the other battery types. However, because the Motocross is a standard AGM battery, I recommend using the Normal Mode.

                                                    BatteryStuff Tech
                                                    February 5, 2013 a 12:09 pm
                                                    • You reference an Odyssey AGM battery having higher charging voltages. What would you recommend for a trickle charger for the PC 680 Odyssey battery?

                                                      May 31, 2016 a 4:44 am
                                                • my girlfriend has a 2000 custon 1200 harley,she has a pigtail charger we cant find the plug in sorce for charging the battery on her bike ?

                                                  February 5, 2013 a 10:01 am
                                                  • Many battery chargers, such as Battery Tender, Pulse Tech, and Battery MINDer use the 2 prong SAE type connector, which is popular for pig-tail style installations.

                                                    BatteryStuff Tech
                                                    February 5, 2013 a 4:26 pm
                                                  • I am installing a backup sump pump using a deep cycle marine battery with inverter. I have a 1.5amp trickle charger to maintain battery charge. We are not anticipating this pump to be used very often. Is a 1.5amp trickle charger large enough to maintain charge?

                                                    February 7, 2013 a 12:33 pm
                                                    • For trickle charging, I recommend using 3% of your battery capacity as the charge rate for maintenance. Therefore, if you are using a 1.5 amp charger, I think that will be okay as long as your current battery is no more than 50 Amp Hours.

                                                      BatteryStuff Tech
                                                      February 7, 2013 a 1:49 pm
                                                    • Thank you for this great information! After studying many articles and web sites, including those specifically from authors writing about my own area of interest in batteries, I believe I found most of my answers (or at least solid confirmations and clarifications) here. But I still have a couple of questions because some of those other writings contradict each other and your material in a couple of ways. In addition, your information doesn‘t really address low amperage usage over cycles that are several hours long.

                                                      What I am hoping to do is use a ready-made portable power pack to run a telescope and hiker‘s GPS unit from a 12VDC cigarette-lighter style socket, a couple of USB powered items, and finally a laptop and possibly a little more from AC sockets provided on the same unit.

                                                      Expected consumption would be as follows:

                                                      Telescope (12VDC) ~0.7 amps for 5-12 hrs/night
                                                      GPS unit (12VDC – not sure, but probably very low draw and only for 5-10 min no more than 2x/night)
                                                      Laptop (110VAC) ~2.0 amps for 3-8 hrs/night
                                                      Cell phone (USB if available on power unit, AC adapter if not ~200mA not every cycle, but when needed ~2 hr recharge)
                                                      Tablet computer (AC adapter probably not used every time – 2000mA for 3-5 hrs when used)

                                                      Several places in your material and others I‘ve read, the statement is made that one should get the highest Ah rating they can. I think these materials have been about higher and possibly shorter-term draw in all cases, but I‘m not sure. Other material says, for the type of low power/long usage above, one should use something with an Ah rating of only about twice what they would probably use in one session on average, so as not to draw the battery down too much in one night, but enough of the total so the cycling is deep enough to preserve battery life by the proper amount of cycling (or something like that ;-). Still other places, I‘ve read that it is better to draw down the battery less (5-10% of capacity) to increase the lifespan of the battery. All of this has me confused.

                                                      I am trying to figure out two last things before I can figure out what I need:

                                                      1.) Should I limit my choice of Ah rating to a lower number (twice my need per cycle) for my kind of usage?

                                                      2.) This may be outside your subject matter expertise, or depend on specific unit features, but I also need to know if built-in inverters draw power when nothing is plugged into them. I haven‘t been able to find anything on that question.

                                                      March 9, 2013 a 8:48 am
                                                      • The truth is, the less you draw down on the battery, the more cycles the battery will provide. There is no golden rule. If you only use 10% capacity at a time, then I say you have spent more money on battery power than you‘re utilizing. If you draw 90% at a time, then have too little battery power and you will find yourself replacing it very prematurely. 50% depth of discharge per cycle is our recommendation because it‘s the most cost effective solution.

                                                        Having any sort of connection (even unplugged) to a battery will technically cause a very minimal discharge, but it is so insignificant, that I wouldn‘t worry about it if I were you.

                                                        BatteryStuff Tech
                                                        March 11, 2013 a 10:01 am
                                                      • Hello! Your site is a fantastic resource!
                                                        I‘m trying to size a multi-bank battery charger for a boat. It will float charge 2 lead acid starting batteries, one generator starting battery, and a house bank consisting of (6) 220AH 6V golf cart batteries connected series-parallel (The house system is 110-120VAC). I have a 5000W inverter and a 7500W gas-powered Kohler generator to produce AC when anchored/underway. The load on the house bank batteries will be no more than 20a (DC), but will vary over my intended use time of 12-16 hours between charging opportunities. Im looking for a fast charge time, because occasionally the charge source will be the gas generator, and the less that runs, the better.

                                                        I suspect my inverter is sized with a greater capacity than my battery bank can safely support. But it‘s what I have.

                                                        I would also love to be able to manually select the charging source for the house bank to switch between the engines’ alternators or a solar array in addition to the generator. Everything is 12V.

                                                        Two questions: Do you see any holes in my plan, and for the charger is my best option to get as many amps as I can afford?

                                                        Thanks in advance!

                                                        March 17, 2013 a 7:33 am
                                                        • Thank you for such an informative site. I‘m trying to ascertain the best and best quality smart charger to buy from you for my motorcycle but have wondered if I need to worry about the fact that I live in a rural area with a lot of power surges. Is there any need to put a power bar/surge protector between the wall plug and the new smart charger? (and/or should this be done to protect the bike‘s expensive ECU ie: elctronic control unit?)
                                                          Thank you.

                                                          April 12, 2013 a 2:27 pm
                                                          • Yes a surge protector will be a good idea.

                                                            Jeremy Fear
                                                            April 12, 2013 a 2:36 pm
                                                          • Nice article because of simplicity. It is a great starting point for people that havent done alot of research, but for me, I had most of this info already. thanks for the article.

                                                            Clever Survivalist
                                                            April 14, 2013 a 2:09 am
                                                            • I have a c-pap machine that I use when dry camping. It is 5 amps, 600 watts. I need a battery that will give me 8 hours of power. Do you have any suggestions? Also, looking for right size inverter to handle the task along with good battery charger.

                                                              Thanks for your help

                                                              May 29, 2013 a 7:41 pm
                                                              • First, because this runs off of 120VAC, you would need an inverter. That will add 15% to the consumed wattage by the C-pap machine, for a total of 690 watts/hour. If you are running that for 8 hours, then your total wattage used will be 5,520 watts. In order to run that off of battery power you would need 883 AH at 12 Volts, ran through a 1000 watt inverter.

                                                                Jeremy Fear
                                                                May 30, 2013 a 8:11 am
                                                                • This seems excessive. Since the Law of the Conservation of Energy applies, then the input power (Wac) must be equal to the output power (Wdc), then since the input voltage in this case is 120Vac and output voltage is 12Vdc, the ratio is 10:1, which means that the current (Amps) must be in inverse proportion to maintain the equal power. In this case, the input current is 5Aac, so the output current must be 50Adc. Since the inverter apparently adds 15% to the power consumption, then the output current will then be 57.5Adc. Since the OP wants it to last for 8 hours, then it seems that the AH rating of the battery would only need to be 460AH (57.5Adc*8H), or a Reserve Capacity (RC) rating of 1104 minutes (8hr*60mins/hr=480mins@25A*2.3 [since the battery has to supply 57.5 A instead of 25A]).


                                                                  We would require more information about your situation.  Please contact one of our techs at

                                                                  Rick W
                                                                  July 21, 2014 a 1:57 pm
                                                              • For a given AGM battery type, find the voltage and constant current for constant voltage and constant current mode of any given volts and amp-hours.

                                                                December 9, 2013 a 3:02 am
                                                                • I have 6 2v 300Ahr agm batteries hookup for 12 v, how many 250 watt solar panel will I need to charger my battery with a MPPT solar controller?

                                                                  May 25, 2016 a 2:16 pm
                                                                  • It depends on what you are trying to accomplish. If your just looking to maintain a fully charged battery pack with no draw coming off the batteries I would generally recommend a panel similar to our Solarland 12v 30 Watt Panel for your capacity. Going any smaller just doesn’t work as well when the batteries get older, and start to discharge at a higher rate. This ensures that a good charge is going to the battery pack daily, and it can get the batteries top off fairly quickly if your have a long stretch of bad weather. If your trying to design a system to supplement energy coming off the batteries then I suggest reading our article Solar Systems the Right Way. This article will get you started in the right direction.

                                                                    BatteryStuff Tech
                                                                    May 26, 2016 a 1:48 pm
                                                                  • I have a Skeeter zx225 boat, 225 Yammy (03)and I run 2 hummingbird 997sihd electronics. I also have a minnkota 36V 101 TM on the bow. Previous electronics were older lowrance units and TM was a 24v system. I have recently upgraded my batteries to sears DH premiums 31m (AH 20/hr rate-100/capacity AH10hr/rate-92; CCA-1150; RC-205. Charger is a noco genius 4 bank (40 amp total). Previous set up had 2 positive wires (6g i think) coming from bow and connected to battery 1 + and the other to battery 2 +…why? I took the one off and just use the main + cable on battery 3 and the neg on battery 1 and +/- jumper between batteries 1/2/3. Does jumper have to be same size as main power wire? what guage do you recommned for jumpers? Does my system seem right…and what is the best way to test voltage output?

                                                                    Scott Ivins
                                                                    April 9, 2014 a 12:07 pm
                                                                    • Dear Tech

                                                                      I am experimenting with a machine that runs on 24v. I want to replace the power supplies for a battery pack. I need about 100 Ah, so Im thinking 2 12v 120 Ah connected in series. My question is: Will a 24V/13A charger do the job on recharging my setup? I don’t have that much experience with batteries. I think it will, but rather ask the expert.

                                                                      June 17, 2014 a 5:43 am
                                                                      • Yes, that charger is in the recommended range of 10-25% capacity.

                                                                        BatteryStuff Tech
                                                                        June 20, 2014 a 12:11 pm
                                                                        • great site i love it ya the best u rock i love

                                                                          July 7, 2014 a 5:47 am
                                                                          • I just purchased two AGM Optima Blue Top batteries (D27M) to use as house batteries on my houseboat (I live aboard). The Optima Blue Top batteries are replacing two wet cell batteries. I have been told I can’t use my current charger (Charles 9000 Series) with the Optima batteries. So now it looks like I need to buy and install a new battery charger. Do you agree? Or can a Charles 9000 Series also charge AGM batteries?
                                                                            My current charger has three “banks”. One for the house batteries (in series), one for the port engine, and one for the stbd engine. I also have a battery for the generator which is not on a charger. If I’m buying a new charger, I’d like to get one with four banks to cover all the batteries. The engine and generator starting batteries are all wet cell.
                                                                            Can you recommend some choices for a battery charger.
                                                                            From the SPEC Sheet for the Optima Batteries (, recommended charging info is:

                                                                            Recommended Charging Information
                                                                            Alternator: 13.65 to 15.0 volts
                                                                            Battery Charger: 13.8 to 15.0 volts; 10 amps maximum; 6-12 hours approximate
                                                                            Float Charge: 13.2 to 13.8 volts; 1 amp maximum; (indefinite time at lower voltages)
                                                                            Rapid Recharge (Constant voltage charger): Maximum voltage 15.6 volts. No current limit as long as battery temperature remains below 125°F (51.7°C). Charge until current drops below 1 amp.
                                                                            Cyclic or Series String Applications:: 14.7 volts. No current limit as long as battery temperature remains below 125°F (51.7°C). When current falls below 1 amp, finish with 3 amp constant current for 1 hour.
                                                                            All limits must be strictly adhered to.

                                                                            Performance Data
                                                                            Cold Cranking Amps: 800
                                                                            Cranking Amps: 1000
                                                                            Nominal Voltage: 12 volts
                                                                            Open Circuit Voltage (fully charged): 13.1 volts
                                                                            Internal Resistance (fully charged): 0.0025 ohms
                                                                            Capacity: 66 Ah (C/20)
                                                                            Reserve Capacity: BCI: 140 minutes (25 amp discharge, 80°F (26.7°C), to 10.5 volts cut-off)

                                                                            July 30, 2014 a 3:05 pm
                                                                            • Due to the fact that we don’t have all the information for your system we would need you to contact us at so that we can ask the appropriate questions, to get you the answer that you may need.

                                                                              August 15, 2014 a 2:45 pm
                                                                            • hi my camper currently runs 2 100ah agm batteries and 1 110ah flooded battery .i have just installed a 100w solar pannel and 10a regultor how should i set the regulator …..for flooded or agm ? my plan is to swap the flooded for agm when funds allow

                                                                              Dave Bort
                                                                              August 3, 2014 a 9:31 am
                                                                              • I have an UB121000 12V 100AH – Absorbant Glass Mat battery and I’m wondering if you can recommend me a good charger for it please?

                                                                                I’m using the battery for a trolling motor.

                                                                                Thanks for your time!

                                                                                April 27, 2016 a 8:59 pm
                                                                              • Very informative. I have a class B motorhome with 4 80 amp hr, AGM batteries, a 2000 watt inverter/charger and a 280 amp high output alternator. The regulator in the alt. is running hot…15.2 volts into the batteries when first charging and I was considering an external 3 stage regulator. Advice? What is the max. volts that the AGM batteries should be charged at?

                                                                                Herb Korn
                                                                                December 4, 2014 a 6:53 am
                                                                                • I would recommend a converter/charger/power-supply around 45-55 amps, make sure it is at least a 3 stage smart charger. A typical AGM battery should be charger 14.6-14.7 volts, however some can take a hotter charge, but you would have to check with the battery manufacturer.

                                                                                  BatteryStuff Tech
                                                                                  December 30, 2014 a 8:55 am
                                                                                • Due to the fact that we don’t have all the information for your system we would need you to contact us at so that we can ask the appropriate questions, to get you the answer that you may need.

                                                                                  August 15, 2014 a 2:46 pm
                                                                                  • Hi, I have a new HP8204B (high power) 24vdc 5A charger, I am using it to charge my 2 × 12v numax SLG63 gel cell batteries.
                                                                                    The light is supposed to turn green when the batteries are fully charged but I have to keep stopping as the batteries are bubbleing and getting hot ? is this ok ? I am not sure if the charger is a 3 stage or not ? some adverts say it is , some just say 24v ?
                                                                                    Thankyou Steve

                                                                                    September 14, 2014 a 2:35 am
                                                                                    • We recommend contacting the manufacturer regarding your charger. Your battery should not be hot to the touch, so the charger could be malfunctioning, or the charger is attempting to charger a battery that cannot accept a full charger and is not timing out.

                                                                                      September 25, 2014 a 11:01 am
                                                                                    • Excellent article. Just wanted to make sure I’m right in thinking I can’t have too high a current from a charger for a battery so long as I don’t leave it charging too long? I bought my son a Peg Perego 12V John Deere Gator ride on for his birthday which comes with a 12V 12AH sealed lead acid battery. The supplied charger is only rated 0.5A so takes an overnight period to charge the battery each time it runs down (leading to an unhappy boy). If I was to buy a higher powered 12V charger (e.g. 8A) I could safely charge the same battery in about 100 minutes based on your formula – is that correct? Many thanks.

                                                                                      Paul Mulvenna
                                                                                      October 28, 2014 a 6:55 am
                                                                                      • The highest amp rated charger for your application would be a 3 amp charger, as you don’t want to exceed 25% of the amp/hr.

                                                                                        BatteryStuff Tech
                                                                                        November 18, 2014 a 2:08 pm
                                                                                      • I’m using solar and have nickel iron batteries at 300ah and 48v. How high should the charge cycle, bulk, absorb and float cycles be. My charge is now at 63.1 volts, bulk is 57.0, absorb is 60.5 and float is 55.1. Is that in the right range?

                                                                                        October 24, 2014 a 7:02 am
                                                                                        • If you have a charger that you can set the voltage depending on the stage, I would suggest talking to the manufacturer of the batteries, so you can charge them based off their recommendation. We sell smart chargers that are already pre-configured based off their history of the manufacturers experience. IOTA has theirs set to Output Voltage Charging 59.04 V, Bulk Absorption Voltage 56.64 V, and Float Voltage 52.24 V. Every manufacturer is a little different, which is why I would recommend talking to the battery manufacturer.

                                                                                          BatteryStuff Tech
                                                                                          November 18, 2014 a 1:06 pm
                                                                                        • Help! No sun for four days and our batteries have dipped below 30%. We live off-grid with a PV array as our only charger. Time to get a genset and charger to keep the batteries healthy. The 12v batteries have a c20 capacity of 546ah. What do you recommend we buy? Thanks in advance, Ed

                                                                                          October 24, 2014 a 9:24 pm
                                                                                          • For charging off a generator we recommend that you pick a charger that does not have an amp rating that exceeds 25% of your total amp/hr. A charger that is more than 25% of your amp/hr could damage the batteries unless they are specifically designed for high amp charging, such as the Lifeline brand.

                                                                                            BatteryStuff Tech
                                                                                            November 18, 2014 a 1:13 pm
                                                                                          • I liked the article, I just purchased a Evolution 1 Tent trailer and the prior owner installed 2 6v batteries for power and also installed LED lights. The batteries are connected in series to produce 12v. What typ of charger should I use to charge and maintain the batteries when not in use.
                                                                                            Thanks Art

                                                                                            November 14, 2014 a 10:22 am
                                                                                            • Art we recommend picking a charger that has an amp rating that is 10% of the total amp/hr. If you would like help picking on out please contact our Tech Department.

                                                                                              BatteryStuff Tech
                                                                                              November 19, 2014 a 2:26 pm
                                                                                            • Hello, I was hoping you could advise on battery charging for a large electric boat project. The battery pack consists of twelve Enersys SBS-EON-190F AGM batteries wired in series for three banks of 48 volts. Each battery bank providing 4×190Ah. I’ve heavy load relays that I may use to wire the three banks in temporary parallel or they could be hard wired together for the 12×190Ah power pack. These batteries require a fast charge cell voltage of 2.40V for frequent heavy discharge. It’s a monster battery pack I know but I’m hoping to achieve recharge in a day or less.

                                                                                              April 16, 2016 a 11:57 am
                                                                                              • It appears you have 48v 570 AH rated battery pack. My highest charger is an <a href="/battery-chargers/48-volt/gel-cell/ICS4820.html">Interacter 48v 20 Amp Industrial Commercial Series Charger ICS4820</a>, which is a work horse, but can only maintain battery packs up to 400 AH. I’m sorry but I don’t believe we have a charger for you. Ideal charging is going to be at about 10% of your capacity so roughly around the 55-60 Amp range for your application.

                                                                                                BatteryStuff Tech
                                                                                                April 18, 2016 a 9:56 am
                                                                                              • We have a catering trailer which has a bank of 6 × 120amp/hr 12v batteries powering an 4000w inverter to run fridges, microwaves etc. The normal consumption is probably only 600w. We have a honda 1000EUi generator which is1000w rated 900w. We run this to charge the batteries. We need a regulated charger of the maximum we can run from this generator, 40amp? What is the maximum we could run? Great site by the way, we have nothing similar in the UK which is where w are based, but the electrical info is international!

                                                                                                Nick Bointon
                                                                                                May 2, 2016 a 11:12 pm
                                                                                                • It will depend on the efficiency rating of the charger/converter power-supply you intend to use. Once you find a brand that you intend to use look to their AC Input ratings. The AC voltage x AC Amperage = The Wattage. The Wattage rating has to be below your continuous run rating of your generator. I hope that helps!

                                                                                                  BatteryStuff Tech
                                                                                                  May 3, 2016 a 6:53 am
                                                                                                • I have a 2 amp 12 volt battery sealed lead acid can I use a charger that have 4 amps 12 volt auto shut off

                                                                                                  January 15, 2017 a 4:32 am
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