I was talking with a friend today who's a dedicated outdoorsman, and he mentioned that he'd been using a solar battery charger on recent camping trips. Like a lot of people, he relies on current from his car while out in the woods. In his case he's got a nice stereo set rigged to his tailgate and he plays music out of it during the day while his friends are sitting around talking and eating. Obviously an inconvenience if the battery ran dry, he leaves a solar battery charger plugged in while the radio's going, and the battery never drains out.
The device is really convenient for him, because he can leave it hooked up all the time. It never drains the battery and it guarantees a start in even the most difficult conditions. Perhaps in a few years it will be standard equipment on new automobiles, so this could be your opportunity to stay ahead of the trend curve.