Let's see, three batteries on boat, same for Toon, one in camper, generator, tractor, mower, 2 for pickup, 4Runner, UTV, so I have to replace several batteries a year, on average.
Truth is, so long as they don't have a draw on them they are fine being stored in the vehicle for 2-4 months. If they aren't fine when you come back, they were likely on their last leg anyway. It's not like we pull the batteries out of our tractors, swather, haybine, or ??? back on the farm either. Why we fishermen think it's necessary to do so is beyond me. Maybe if I stored my boat in Sept and didn't look at it again until June I'd think differently. I do clean the terminals at least every other year. That's about the extent of it for me.