Batteries lifetime is measured in the number of charge/discharge cycles not time. Used for electric flight with high discharge and usually fast charged all the time something around 100 - 200 cycles may well be all you get out of them. That would be quite a lot of flying for one season but it's not impossible.

It's worth cycling them with a slow C/10 charge a couple of times. That can sometimes balance them up and bring them back to life.

Steve