Ed Majors

Thanks, I have done that. All other batteries check out fine and the charger tests fine. Somehow over time, the middle bank somehow reverses polarity on that one middle battery. It works fine for 2 or 3 months, then without warning the middle battery starts showing negative volts. This negative 12v subtracts from the positive 24v of the other 2 batteries. This leaves 12v going to a 36v trolling motor. So it quits working altogether.

Thanks for all the responses! Some great advice. I have tried most of it and no change. I don't trust my middle bank on the charger since it seems to have ruined 2 new batteries. I have it disconnected and charge that battery with a separate charger. I will see what happens before replacing the onboard charger. Thanks again!

I have a 3 bank onboard charger connected to my 3 trolling motor batteries. They are connected in series to run a 36V Fortrex TM. Suddenly, the trolling motor would not run and upon checking I found one oy my three batteries was showing - 12.84 volts(as in minus negative voltage). I had not changed any connections and verified all battery and charger connections were correct. I took the battery to Interstate and they agreed it read negative volts and had no idea what caused it. But they replaced it under warranty. My first thought was the charger was bad and took the boat to a dealer to replace the charger. He checked it and said the charger was working fine!This was all back in February. Everything was fine with the new battery. I didn't use the boat alot this summer, just an occasional fishing trip or boat ride. I kept it charged up regularly. Then today the TM would not work again. I checked and the same (new) battery shows negative volts again. What would be shorting this battery out? Thanks for any help!