I charge all our batteries before putting them out if I can that seems to make a difference.
Using 12 volt gel cell batteries I can run nearly the whole season feeding 2 times a day with no solar charger and no recharging.
If you will pull your batteries out and charge them (even if they are on a solar charger) onece a year or so they will probably last longer. I have a 12 volt feeder that's been going for 3 years with the same battery on a solar panel and its running like a top.
Also find a good charger with a float setting so it will not overcharge your batteries, the battery life will be much longer (many more drain/recharge cycles).
It's hell eatin em live