12v marine battery with reverse polarity????

Geo-TH,In

Well-known Member
BIL has a vacation home on lake Esutas in Florida.

He calls today and says neighbor's trolling battery has reversed polarity and is only putting out 9v. Yes, the positive is negative and the negative terminal is positive.

There are 2 12v marine batteries in series to power the 24 v trolling motor. There are 2 12v chargers hard wired to change the 2 batteries. Has worked this way for years. So he asks how can this happen? I told I don't have a clue.

Later I called him back with a theory, but told him it like asking a DR over the phone for a medical opinion. He needs to send me round trip tickets so I can see first hand what's wrong. And the fishing better be better than it was when I was there before Christmas.

So, what's your theory as to what happened?

His neighbor is went to town to get a new battery so there are no testing the battery.
 
Hello Geo-TH,In,

Probably just a bad battery? He is disposing of the evidence. Twice as hard to guess now! I would certainly make sure that the charger is not the culprit. That's my guess,

Guido.
 
One charger quit working, so only one battery got charged. The low battery went totally dead then was reverse charged by the full charged one.

You see that in cordless tool batteries where the owner discharges them to the last gasp of the tool.

The weakest battery cell goes dead first and the remaining ones reverse charge that dead one.

Many of those little cells only need a little reverse charge to wreck them.

Thats why many saw to quit discharging a tool battery when the tool first starts to slow down.
 
A battery can be charged in reverse, if it is dead or very low and connected in reverse, to the charger.
 
We used to do this on purpose in a last ditch effort to get a few more months of life out of old wet cell batteries. Discharge it fully , charge it in reverse , discharge fully again , then charge with correct polarity. This was supposed to dislodge deposits from the cell plates and restore some charge capacity . It did work after a fashion , especially for low drain work like electric fence chargers . Doesn't work at all with gel cells though .
 
Jon, That's what I told my BIL. The charger connected to the bad battery either quit or the connection came lose. The good charger back fed through the motor some how and caused bad battery to reverse polarity.

By the time I told him to try to charge bad battery with another charger, the guy had already left to buy a new battery.

I told BIL to use amprobe to make sure each charger is working. Yes an amprobe will work on a battery charger. If you don't believe me, try it.
 
(quoted from post at 17:31:01 02/24/15) Jon, That's what I told my BIL. The charger connected to the bad battery either quit or the connection came lose. The good charger back fed through the motor some how and caused bad battery to reverse polarity.

By the time I told him to try to charge bad battery with another charger, the guy had already left to buy a new battery.

I told BIL to use amprobe to make sure each charger is working. Yes an amprobe will work on a battery charger. If you don't believe me, try it.

Buddy had better purchase two new identical batteries. or he is just going to reverse polarity the existing "good" battery.
 
We work on tornado sirens with 4 12v batteries in series. They have individual chargers with a unreal wiring lash up. A bad connection or charger and a battery will get charged up backwards. Some of the time we can salvage it. Have to run it down all the way and still the new chargers will not charge it so have to put jumper cables on then put charger on.
 
Why not put all the chargers in series and make a 48v charger out of 4? That way if one charger dies, nothing will work. No battery damage?

Or why not buy a 48v charger?

Why didn't they use a 24v charger instead of 2 12v ones in series? This almost sounds like something Bubba would do.
 
Geo, they probably use 4 12's for redundancy. They probably don't get checked that often and if one fails the safety system will still function. It is a tornado warning siren we're talking about in this case.
 

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