battery reversing polarity

[curtisce]

I bought all new batteries last spring. Was looking to buy diehards ended up with Duracells, they both start with D and actually look quite similar. They worked fine all last season. No problem with the cranking battery running livescope. They are AMG.  I have only a 2 bank charger so At the storage unit I put one bank on the cranking battery. Last week I went out to put some stuff in the storage unit. I took the charging cables off the cranking battery and put it back on the trolling motor battery. The charging unit red light came on when I plugged it in meaning bad connection, Messed around with the connection at the battery but no change. Brought out my other battery charger from home hooked it up and it said wires reversed and wouldn't turn on. Brought out a voltage meter that my electrician friend instructed me on how to use. Hooked it up and the one battery reads -6 volts. When I reversed the meter, put black oon + red on - it read +6 volts.The other 2 batteries read +12 volts.  Anyone ever hear of that? Brought the battery home and will take it back where I bought it when the streets get a little clearer.

[gotmuddy]

if its 6v then it wasn't getting charge.

[curtisce]

14 minutes ago, gotmuddy said:

if its 6v then it wasn't getting charge.

It is  reading minus 6 volts. The charger won't charge because it thinks I have the cables hooked up backwards

 

[gotmuddy]

16 minutes ago, curtisce said:

It is  reading minus 6 volts. The charger won't charge because it thinks I have the cables hooked up backwards

 

batteries cannot have negative voltage.

[gotmuddy]

10 minutes ago, gotmuddy said:

batteries cannot have negative voltage.

well this is partially true.  apparently its possible for the polarity of a battery to change:

 

https://www.panasonic-batteries.com/en/faq/why-does-battery-show-minus-voltage-when-checked-voltmeter#:~:text=If the poles of your,phenomenon called “polarity reversal”.&text=In this case there is,old and new batteries together.

[fishinwrench]

Yep, a severely overcharged battery can reverse polarity.   As can a dead one that someone just refuses to give up on....and keeps trying to charge it.

So can one that's been in a fire.....so I've heard.  

[tjm]

First, disconnect the battery completely before using the voltmeter on it, if it's still connected to anything the meter  will read the system rather than the battery.  Check that the leads on the voltmeter are not reversed on the meter itself. And on a multimeter that the switch is in "DC+" rather than "DC-" -stupid stuff I've done- use the meter on a known good battery as a test of the meter.

I've never seen it, but in theory, I know  a couple of ways to get a wet battery to charge backwards, both involve a completely dead battery and actually hooking the charger up wrong. It's likely that if this happens the battery is shot. Full discharge and very slow correct charge might work to restore it, but I've never tried that.  I  have seen a car battery explode when jumpers were being hooked up, so explosion is always a consideration.

maybe just bring it back where you got it and let them do the testing, they probably have a way to load test and determine damage

[tjm]

3 minutes ago, fishinwrench said:

severely overcharged battery can reverse polarity.

That's new to me, I thought they just boiled dry or melted. 

[fishinwrench]

28 minutes ago, tjm said:

That's new to me, I thought they just boiled dry or melted. 

I had a boat brought in that had a tach not working and a voltage regulator fried.  It was a Merc and the VR got backordered.  The guy insisted on doing a dam-to-dam run (Bagnell to Truman and back) that he had planned......So since the motor started and ran, he went ahead. (Against my recommendation!).

Halfway back he had to be towed in, and of course he brought it back to the shop.  Stator was melted, wiring harness was toasted from motor to console, and the battery was reversed.  

4000.00 bill, and I got to say "Told ya so!" 😏 

That battery cooked at 40 amps for 12-13 straight hours. 😳

[tjm]

WOW!!

I would have expected most of that, but not the reversing of poles. I wonder if the wiring meltdown caused a cross wire effect, I had a entry wire melt on a mobile home that fed both sides of the fuse panel from one leg of the 220. And I've seen under dash melts in trucks that caused hot and not to be crossed over.