Has anyone tried one of those solar-cell battery 'topup' units I see advertised? You plug it into the cig lighter and leave the solar panel on top of the dashboard. It is supposed to keep the battery fully charged and extend its life... My truck is precomputer (76 F250) so I'm not worried about buggering up a modern ECU module. Our old girl sits around too much and batteries don't last more than about 3 years due (I'm told) to "sulfating".

 

Ive seen them used at car shows and whatnot to keep batterys charged up with the doors open, and they seem to help.

 

If you park it near an electrical outlet, I've had good luck with a device called a Battery Tender. It's basically an automatic trickle charger, and it's designed for what you want to use it for. Can't remember what they cost, but I think it's somewhere between $50-100 US. A bit more than the solar ones, but it will also recharge a completely dead battery, which I doubt the solar ones will do.

Just a thought.

*If you do get a solar one, post up how well you think it works- I'm curious.