BillConner wrote on Apr 5^th, 2011 at 7:17pm:

Not a car guy but couldn't you do this backwards through the cigarette lighter (or whatever is the politically correct name for it today)?

I think you may be on to something :-/
We have some electrical engineers here, maybe they could give their expertise? If you could it would beat messing around under the hood ;)

A quick Google check answered our questions.
There is a myriad of solar panels with adapters that charge 12v battery from the cigarette lighter. The better have a diode that prevents reveres drain. Some fold, some roll up. Not cheap, but since you can use them for marine/camping applications, might be worth it in the long run if you worried about dealing wiht a dead battery in a remote area.