I took a trip to our local Harbor Freight Tool store, and they have an inexpensive solar battery charger. Well, relatively inexpensive. Around $20 for a trickle charger that won't cook the battery. I saw a post a bit ago where someone had bought a similar one that they use on VW's when shipping them here. Sounds like a good idea.
It is made by ICP Technologies. They are big in Solar accessories.
I may try it out on my car that has a battery that is slowly on it's way out. With the Florida sun, I should do OK.