If you are a boater, you likely have at least 3 batteries on your boat, maybe 4. Unfortunately, battery issues usually do not happen in your garage, they occur at the lake while fishing, and probably during a tournament. It is possible to have a battery that charges fully to 13 volts, but no longer has the stamina to hold that charge sufficiently. Here is a way to test that battery. This is a carbon-pile load tester that I got on Amazon for $20. I tested all 4 of my batteries and found one that was not holding a charge, no wonder my trolling motor was acting sluggish. You can also use this to test the charging system. I discovered the alternator on my truck was not working properly. This is a must have for any boater.
Fishing Wednesdays, not weekends.