The boat batteries are in the basement where there is a cool but constant temperature. They are also on a slow charge to keep the voltage at proper levels. Don't forget to look at the water once a month and use distilled water to fill. The camper batteries are still being used with the camper plugged in till we move south.
I like (The 12volt Side of Life) part 1&2.
http://www.marxrv.com/12volt/12volt.htm