[Dave S.]

The solar powered idea isn't bad. I've seen them used to keep batteries on car trailers charged up ( to power battery operated winches).
I only drive my car about once a week during the summer and I never have to charge the battery during the driving season. In the winter I use a plug-in Porsche charger that connects into the cigarette lighter socket to keep the battery maintained. So if you drive it every weekend, you'll probably be OK without a charger.