TM Battery Problem

[53orbigger]

I am looking for some trouble shooting advise before I go and spend another $150 on a new battery that may or may not be the problem. I have a 24V system running on 2 size 27 AGM batteries. The last time out the trolling motor would only last about 3 hours before needing to be recharged, whereas in the past I could go all day. When I plugged it into the onboard guest charger it would charge as usual and eventually I would get the green fully charged light. I had the batteries tested, what I assume was load testing, at my mechanics and he informed me that they were both good. I went back out fishing and after a couple of hours tested the batteries with a digital voltage tester and found that one battery was at 12.8 volts and the other was at 10.8 volts. This tells me that the battery reading 10.8 is bad, but my mechanic told me it was good and I don't know much about batteries. So, my questions are does it sound like a bad battery or maybe charger and is there a better way to test an AGM battery to see if it has a bad cell?

Thanks

[Northlander]

Read my post about this. My batteries tested good until I took them to Interstate and they checked them. They were bad. I got 2 new ones and I go all day long now. It took Interstate to put it under a load to get true results. I dont know why theirs showed the flaw when the local auto shop didnt. I guess I would get 2 good bateries from a friend and see what happens then. If thats not the issue the next one would be to test the on board charger.

Oh and get 2 new batteries of the same type not just 1. The 24 volt system is only as good as your weakest battery.

[PerchJerker]

I had the batteries tested, what I assume was load testing, at my mechanics and he informed me that they were both good.

My guess is that he didn't test them under a load. What you are describing is typical of a bad battery, it shows full charge / full volts but it has minimal capacity to maintain that voltage.

[53orbigger]

Thanks guys. I appreciate the help.