Comments on: Battery Myth | Can a Battery ‘Reverse’ its Polarity?

By: Byron

Byron — Fri, 25 May 2012 07:02:30 -0700

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.

By: Byron

Byron — Fri, 25 May 2012 07:18:02 -0700

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?

By: Tech

Tech — Fri, 25 May 2012 10:23:41 -0700

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.

By: Sam W

Sam W — Thu, 31 May 2012 08:33:24 -0700

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

By: Tech

Tech — Thu, 31 May 2012 09:12:44 -0700

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.

By: Jay

Jay — Sun, 18 Nov 2012 05:58:14 -0800

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

By: Tech

Tech — Mon, 19 Nov 2012 14:32:53 -0800

Was the battery reversed in polarity before of after the installation?

By: Paul

Paul — Thu, 25 Apr 2013 18:44:08 -0700

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.

By: TRU

TRU — Tue, 14 May 2013 15:43:59 -0700

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!

By: Vincent

Vincent — Mon, 27 May 2013 14:38:22 -0700

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.

By: Jeff

Jeff — Wed, 04 Dec 2013 13:38:23 -0800

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…..

By: wieger

wieger — Fri, 13 Dec 2013 06:27:41 -0800

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.

By: Graham

Graham — Mon, 20 Jan 2014 00:00:37 -0800

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.

By: Kelly

Kelly — Tue, 04 Mar 2014 17:18:13 -0800

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.

By: Tony Bowen

Tony Bowen — Mon, 24 Mar 2014 01:01:42 -0700

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!

By: N. Head

N. Head — Mon, 14 Apr 2014 07:46:09 -0700

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..

By: dave

dave — Sun, 29 Jun 2014 13:18:17 -0700

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

By: Mario

Mario — Tue, 26 Aug 2014 08:57:07 -0700

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?

By: tim

tim — Wed, 27 May 2020 10:51:54 -0700

the battery in my 95, civic del sol just reversed itself. the only thing i did was keep it charged with a Battery-Minder charger / desulfater which i've been using for years with no problems. i am currently using it on other batteries with no issues..... i tried the Battery-Minder on it one last time and it signaled, "polarity reversed". i checked the battery with my voltmeter and sure enough, it's reversed.

By: Tommyguns

Tommyguns — Thu, 25 Jun 2020 17:28:51 -0700

YES it's POSSIBLE I did it I now have a battery that the negative is positive and positive is negative.I used a old charger that wasn't red and black cables so when I hooked up the positive to the negative of battery it didn't spark because the battery was so weak AND NO The battery doesn't need to be dead for this to happen the battery I used was 10.4 volts it was low and a bad battery but know where near dead somehow overnight it reversed polarity and I awoke to find a battery that was 12.5 volts using a smart charger to check it but it took me a while to figure it out as the smart charger kept saying warning reverse polarity eventually I said F it I put the red on black black on red and the smart charger then said GOOD battery..Will prob give it to my daughter to show at science project..But 1st I will attempt to return battery to orig state attempting to reverse polarity to see if it can be returned to normal wich in sure It will..

By: Brett Bouttell

Brett Bouttell — Fri, 03 Dec 2021 16:45:08 -0800

Thanks for the info very helpful