Okay, just for the record, I'm not storing them on the concrete floor of my garage, but not because I was concerned about the batteries discharging. I have them on a furniture dolly so I can roll them around whenever I need to move them. When I took them out of SittEscape, I was amazed at the weight of each battery. I guess it's been a long time since I moved the battery, even in my cars. Hey, shouldn't a 6 V battery weigh half of a 12 V battery?
Anyway, I didn't want to have to struggle with them during the off-season. I connected a very simple Schumacher's Speed Changer battery maintainer from Wallyworld. Once a week or so, I switch from one battery to the other. Seems to be working just fine, although it's only been a month.
Thanks for all the friendly advice and banter.