battery/trolling motor problem

[fasternu]

I have a Minnkota 12v 55 lb thrust bow mount. I was using it and it ran great, then after about 35 minutes, it slows way down, and the battery reads dead. I let it sit for about 30-45 minutes, the battery reads 2/3 full, and the motor works fine again for a bit, then repeats this problem.

I figured it was a bad battery, so I charged it, then took it and had it load tested. They said it was fine.

My question is, could the battery still have a bad cell or something that would allow it to read fine, even though it doesn't hold a charge, or do you think I have a short with the trolling motor.

I have a 40 amp breaker on the hookup. Should I try a 60 amp braker?

[jeffreyd]

Is the breaker popping? If that is not happening then the breaker is fine. I would suspect that you have a bad battery, my question would be how did they do a load test? was it with a digital load tester or an old style toaster type?I would also check the connections for the ground, you could be lossing some conductivity there. Good luck

[fasternu]

Ground is good, I already checked. No, the breaker isn't popping, but it is getting warm. The load test was done on an old style tester. I think it's a bad battery as well, just trying to be sure. Thanks for the help.

[marine_man]

It sure sounds like a bad battery to me as well.

marine_man

[Dale Rueber]

Standard load testing is not a good test for deep discharge batteries. Load testing only tests the cranking amps which is the immediate surge that the battery is capable of producing and in my experience has little to do with the reserve capacity. While it will tell you if you have a bad cell it will not tell you anything about the reserve capacity.

Last summer my trolling motor battery would not run very long so I took it back to the store where I purchased it because it was still under warranty. The load testing came back within what the manufacturer specified so they would not cover it. Bought a new battery and it lasted 3-4 times longer under the same load conditions. I wrote the manufacturer but received no response.

To my knowledge the only way to test reserve capacity is to drain the battery slowly and measure the output.

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