Batteries Reversing Polarity?

[Cliffprocraft190]

I recently installed new batteries and a Noco Genius Pro 10x3 charger in my boat. I hooked everything up and plug it in. Bank one threw a warning light that was for hooking the battery up using the wrong polarity, but it was hooked up correctly. Two of the batteries are connected in series to give 24 volts for the trolling motor. When I took the jumper cable off, then everything worked correctly.

I called Noco today and explained what happened. Their tech support said it should charge with a bank hooked to each 12V battery even with the two connected in series. He said to switch the batteries on bank 1 and bank 2 and see if bank 1 still said polarity was backwards. He said, if so, then something is wrong with bank 1 of the charger.

He said batteries can sometimes reverse polarity and to test the battery that caused the warning with a voltmeter and if it showed negative voltage, then the battery had reversed polarity; otherwise, something is wrong with bank one of the charger and they would warranty it.

Sound right? I didn't know a battery could reverse polarity. I always assumed batteries had fixed polarity and that the polarity was as marked on the case.

Of course, now I can't find my voltmeter!

[SteezMacQueen]

It would be a new one to me if it did that. Lol

[MichAngler]

In all my years I have never heard of that
I’m not saying it’s impossible but it’s more likely he’s yanking your chain

[Transom]

Unless there is some weird chemistry thing going on there that I have never heard of I am confident in saying guy was giving you some BS.

He is correct that a negative voltage would give you a reversed polarity voltage but I am unaware of any reason you should get a negative voltage on a marine battery with the leads properly connected.

[mean_dean]

I've never heard of that happening. Quick google search...

If you have a wet cell battery are filling it for the first time, and are using an old style battery charger, 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.

[billnorman1]

It sure can happen. If for instance a battery is one in a series circuit and it goes dead, and the load is still applied, the current in the circuit can charge it in a reverse direction. Normally it only reverses one or two cells.

[H-D Dad]

I've seen it, usually when a person replaces 1 of 2 dead batteries in a 24 volt system that older deader battery can change polarity.

[Cliffprocraft190]

It was a lithium battery. I don't know if that makes any difference, but the tech said it happens more with batteries connected in series.

[Cabman1880]

I recently installed new batteries and a Noco Genius Pro 10x3 charger in my boat. I hooked everything up and plug it in. Bank one threw a warning light that was for hooking the battery up using the wrong polarity, but it was hooked up correctly. Two of the batteries are connected in series to give 24 volts for the trolling motor. When I took the jumper cable off, then everything worked correctly.

I called Noco today and explained what happened. Their tech support said it should charge with a bank hooked to each 12V battery even with the two connected in series. He said to switch the batteries on bank 1 and bank 2 and see if bank 1 still said polarity was backwards. He said, if so, then something is wrong with bank 1 of the charger.

He said batteries can sometimes reverse polarity and to test the battery that caused the warning with a voltmeter and if it showed negative voltage, then the battery had reversed polarity; otherwise, something is wrong with bank one of the charger and they would warranty it.

Sound right? I didn't know a battery could reverse polarity. I always assumed batteries had fixed polarity and that the polarity was as marked on the case.

Of course, now I can't find my voltmeter!

Wow, this is crazy. Glad I saw this post as the same thing just happened to me. I replaced all my batteries on the 2023 Pontoon boat we bought so I wouldn't have any battery issues. I too bought a Noco Genius 10x33 last July. I went to take the Pontoon out last week for the first run since November and one of the banks was showing a red code that turned out to be reverse polarity and my 24 volt trolling motor would not work. I thought I was going nuts. Battery read out at 11 volts but the trolling motor would not even turn on. Looks like I will be calling Noco if the battery is good. I did switch banks and still got the reverse polarity red light. I will put a verified good battery in line tomorrow. Hope it's the charger and not the battery, but switching banks should have solved it I would think?

[Brianmoore25]

Seen it several times on trolling motor batteries in series.

[jgorrell.tcp]

I had it happen with an impulse lithium trolling battery. Bill had me do a couple quick test and replaced the battery asap. I could unhook the battery and it would flip back but would flip if it went unused for a couple days.

[1958]

If you can't find volt meter you can rig up anything that works on 12 volt with wires. It's just to test polarity not volts.
My first thought was wonder if battery was made backwards or something

[CJ1]

I had it happen with an impulse lithium trolling battery. Bill had me do a couple quick test and replaced the battery asap. I could unhook the battery and it would flip back but would flip if it went unused for a couple days.

This is good to know, I have seen it with lead acid but did not know Lithium could do it. Would have figured the BMS would have stopped it. Did he give you a reason? With lead acid they have to be discharged and current reversed as was stated. Cj

[Cliffprocraft190]

Well, I switched banks today on the two lithium batteries while they were connected in series and the charger did not light up any reversed polarity warnings. I ran my trolling motor a little bit and everything seemed normal. I still could not find my voltmeter, so I could not test the individual batteries.

Now I wonder if I should just fish for a day and then see what happens when I plug it in to charge again. Post #11 has me wondering if it will just happen again on the same battery and I will have to get a warranty replacement on the battery.

[billnorman1]

Maybe it's time:
https://www.harborfreight.com/electr...ter-64014.html

[Cliffprocraft190]

Found my voltmeter. Removed the jumper cable connecting the two lithiums in series and checked voltage on each battery separately. The battery that had been originally connected to bank 1 tested +12.66 volts and the battery that had been originally connected to bank 2 tested +13.25 volts.

Now I'm wondering why bank 1 threw a reversed polarity warning when I used it for the first time. Just a fluke? or will I have issues down the road? Have my first tournament of the year next weekend and don't want any problems with trolling motor performance.