Batteries, Chargers, and More

Battery Myth | Can a Battery ‘Reverse’ its Polarity?


Actually, yes, but not without help. Reversing the polarity on a battery can happen only a couple of ways. 

Charging a Battery in Reverse

If you have a wet cell battery are filling it for the first time, and are using an old style, non smart charger, and short the terminals while you are filling it, yes it is possible to hook up the charger backward and reverse charge it. You would not necessarily notice a spark because the battery gains voltage as the battery is being filled, and if it is being charged while you are filling it, the short would not be a strong enough discharge to create a spark.  If that was to happen, and a charger was hooked on backwards, or if it was installed in a kick start vehicle and hooked up backwards, then you can end up with a battery that has been charged, but backwards.  Notice there are a lot of ‘ands’ in the above scenario. This situation is possible, but not very likely.   

The second possibility is reversing polarity after the activation process. This is also rare, as it requires a sequence of errors to be present after the installation of the battery. The only way for this to happen would be to completely discharge the battery, either by leaving the key on, or by an unnoticed dead short that completely dissipated the charge over a few days.  After that happened it would appear to be a dead battery. 

Remember, a completely discharged battery is nothing more than an empty vessel.  In order to gain a negative charge, it would then necessitate being hooked up backwards, and charged that way. So the real question here is: how can a battery reverse polarity after it has been installed?  That same previously discharged battery would then be vulnerable to reverse charging, either by connecting the battery charger backwards, or by a charging system that reversed polarity (very rare, but still possible). 

So let me restate: The only way for a battery that has a positive charge, to reverse itself, is for the battery to be completely discharged, and then reversed charged.  We have seen this happen a couple of times, and it would be considered the more common of these rare situations.   

For all intents and purposes, the battery will be ruined.  You could technically charge it up, negatively, and continue to use it, but your plates are designed with the positive plates being lead dioxide, and the negative being composed of a sponge lead, which would now be reversed.  Because the reversed battery is no longer formatted correctly, it will only work to a limited degree. The fact of the matter is, a lead acid battery cannot reverse its own polarity without an external stimulus. It is just not possible.

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  • When I pulled my boat out a few weeks ago, the batteries were dead, because I forgot to unhook them at the end of last season. I have 2 batteries in parallel (negative to negative; positive to positive), with a switch, 12-volt system. I put a charger on one battery to start my boat (switch set to both batteries). After running, boat wouldn‘t start. Pulled both batteries out. One measured +11.7V and the other -6V! How does that happen? I take it from your article that I should replace the battery with reversed polarity. Thanks for your reply.

    May 25, 2012 a 7:02 am
    • Batteries can only be reversed in polarity if they meet this criteria: They have to be completely discharged first. So with your batteries in parallel, one battery was probably drained further than the other. Both were used up but one went dead first. Discharged battery plates are essentially neutral, so when both batteries were recharged together, the plates in the dead battery swapped chemistries, and consequently polarity. Replacing that battery is advised.

      May 25, 2012 a 10:23 am
    • I had two batteries connected in parallel with a switch (set to both) in my boat that were dead. I jump started my boat and it ran fine, but couldn\\\‘t get to restart. Pulled batteries out and one read +11.7V and the other -5.9V. How could that have happened and can I salvage/reverse polarity of the other battery or is it ruined?

      May 25, 2012 a 7:18 am
      • With the batteries in parallel it is essentially one big battery now and should be wired to charge and discharge accordingly. (positive line out off of one battery and negative line out from the other battery) This will also achieve a better and correct charging method as the charge goes across both batteries as opposed to one battery then to the other if both of your line outs are from one battery and the other battery is just \“jumped\” to the first one. So in the reply, \“one being drained further than the other\” that should not hold water if the batteries are wired correctly. Otherwise i agree with the replied stated cause and remedy. Great article and post!


        Sam W
        May 31, 2012 a 8:33 am
        • You‘re correct, in parallel they behave as one unit. But if the batteries were not evenly charged to begin with, it is possible that one will run down first. This is common in marine applications where there is a switch to use one battery, and then both. In this case, one battery is always being used, while the other only drains when the switch parallels them.

          May 31, 2012 a 9:12 am
        • Switched pos neg terminals on installation on a marine bat number 2…
          Dual bat with a switch… There is a short in the wiring I think on bat two….I have replaces the batteries, switch alternator….
          Where should I start…thanks any help,would be appreciated

          November 18, 2012 a 5:58 am
          • Was the battery reversed in polarity before of after the installation?

            November 19, 2012 a 2:32 pm
          • My motorcycle battery has a reverse charge due a problem with my charger reversing polarity I presume. It kept blowing fuses when I hooked it up a few days ago and when I took it to the shop they said it is reversed. A new battery is not blowing the fuse.

            April 25, 2013 a 6:44 pm
            • I switched the terminals accidentally and shorted something out (I think maybe the alternator) and now when I go to connect the battery it sparks a lot…and if i disregard the spark and put it on anyway it starts to smoke where the alternator is. What did I do & how do I fix it? Plz help!

              May 14, 2013 a 3:43 pm
              • My friend accidentally reversed charged a new wet cell car battery. Would totally discharging the battery, then recharging it correctly save this battery, or is it toast! Thanks for your comments.

                May 27, 2013 a 2:38 pm
                • I somewhat agree with the article. Though, the chemical reactions of the battery are completely reversible. The battery, as stated, must be completely dead for this to happen as when a battery is completely charged one set of plates (Anode)- is composed of Pb (or plain lead) and the other (cathode)+ is composed of PbO_2 or Lead-dioxide. The chemical reaction for discharge is as follows:

                  (Anode)- Pb + HSO4− → PbSO4 + H + 2e −

                  (Cathode)+ PbO2 + 3H + HSO4− + 2e− → PbSO4 + 2H2O\’

                  As you can see in these half reactions, both sets of plates become PbSO4 or Lead-Sulfate, thus a completely discharged battery would essentially be a \“clean slate\” that could be charged any direction you like (in an ideal scenario). But, as it is unlikely to have a \“completely\” discharged battery 0V, as the article said, it is also unlikely for this to be a very successful operation as it requires special current control factors…..

                  December 4, 2013 a 1:38 pm
                  • What happens if you have a 24 volt system (2×12 volt in series.)(although same capacity different brand and age). Is it possible that after running dead after a long time that one (the newer one) is at 11.3 V and the other (the older one) is at – 8.2 V ? It has been said to me that nobody has touched the batteries in the mean time. I am confused.

                    December 13, 2013 a 6:27 am
                    • I have just charged up an Exide 12v motor cycle battery. It was brand new but old stock and had 4.5v. I charged it up overnight with 12.85v recorded in the morning. I disconnected the battery charger clamps while I went out. When I came back I decided to just give it a bit more charge and when I connected the battery charger clamps to the battery my chargers amp meter went wild. I checked with a multimeter and found that positive was negative and vice versa. I did nothing wrong with the charging, I am heavily into electronics and know how to charge a battery. This switching from positive to negative happened when I was out for an hour and there was nothing connected to the battery.

                      January 20, 2014 a 12:00 am
                      • This just happened to me, when I pulled the charger it showed 12.7v, but when I went back 5 minutes later and tested it with my multi-meter the polarity was reversed.

                        March 4, 2014 a 5:18 pm
                      • My truck sat for about 4 mths cause I was working out of town. When I came home the battery was dead,charged it an put it back in, all my electrics went reverse. Meening , down button on the windows,they went up. Anyway I figured it out. My battery had reversed polarity. Go figure!

                        Tony Bowen
                        March 24, 2014 a 1:01 am
                        • I had a duff Jumpstarter that said charged but wasnt, took it to bits saw nothing wrong attached my good jump starter to the duff ones battery plugged the duff ones charge wire in and turned on that didnt work so i swaped the polarity from good to duff (pos-neg neg-pos) it now charges..

                          N. Head
                          April 14, 2014 a 7:46 am
                          • Yes u can still use the other battery, but u are to use it according to its changed current polarity. So your negative is now your positive and your positive is now negative. Use a colored marker to mark the new polarities to prevent future errors in connecting the battery

                            June 29, 2014 a 1:18 pm
                            • I have a nicely restored \‘69 Camaro that is stored in my garage between car shows. I always disconnect the Negative Cable from the Battery while not in use and I attach a Battery Minder I purchased through The Eastwood Co. It has a couple of LED lights on it that tell me everything is hooked up right and charging correctly. It will NOT work if the cables are reversed. So I know it was attached correctly when I parked it last. After the last car show I attended, I parked the car, disconnect the Negative Battery Cable and attached the Battery Minder as I have done many times before. All LED Lights on the Battery Minder showed \“OK\”. When I went to get it ready for an upcoming car show, I disconnected the Battery Minder and connected the Negative Cable. The Negative Cable \“Sparked\” when I connected it to the Battery Terminal and the 10 AWG Wire from the Positive Battery Cable started to smoke and melt. I thought I had developed a \“dead ground\” somewhere in the harness, but after more than 20 hours of diagnosing the problem, I discovered that the Battery had reversed its polarity! The Battery is about 4 years old. The Battery reads -12.53 Volts. Based on this article, I did not have the right conditions for the battery to reverse its polarity. The battery was not completely discharged and the Battery Minder was not reverse charging. What could have possibly caused the battery to reverse polarity?

                              August 26, 2014 a 8:57 am
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