Trolling Motor Battery Question?

[Duke1947]

I have a 2005 Bass Boat which has a straight 24 volt, 71 pound thrust Motor Guide Trolling Motor. Last year, I experienced a problem with one of the two dealer installed trolling motor batteries failing in less than a year of use. The batteries were Interstate Trolling Motor batteries and I was told that they have a reputation for not holding up. I had to replace one of the Interstate Batteries and get a new one. My trolling motor batteries are hooked up to a Dual Pro SE (2) bank charger. Lately after charging my batteries immediately after a fishing trip, the charger lights go to green and the batteries appear charged. Yet, after approximately three to four hours of use, the power drains and I am about running on one battery for the rest of my fishing time. I do not believe it's in my charging system. I was told last time that there was a way to check the battery power to determine if it's the battery, but I can't remember what to do? I need to determine if it's the battery (the remaining old one, or possibly the newest replacement or it might be the charger? Can someone help me? Any information would be appreciated!!