Can you answer some more basic questions?
- How many batteries did you use this season?
- Did you have a process for use such as a serial number and a cycle schedule?
- Were you fully charging batteries before taking them off the charger?
- Were you putting them back on charge immediately after use?
- Did you Battery Beak them before and after use?
- Did you maintain their charge through the pre-season?
- Did you fully charge them before first use?
You easily can kill batteries by the method you described if you are not cycling (keeping an even usage) and charging them appropriately.
I'm paging our battery experts. Hopefully they will chime in soon.