Good afternoon, Rusty!
I had never heard of a solar battery charger prior to your mentioning it! 
It could well be the answer to our problem, too?
I have no idea  whether our cigarette lighter functions when the ignition is off.......no one ever uses it!
I shall pass all this on to my husband, and if he fancies the idea (I think it's a good one) he can have  a word with our mechanic friend.
At present, my husband has  to take the car for an extra little "outing", ever  so often, just to keep the  battery going.
What are you up to, today?
Are you watching the Tour de France  and /or golf?
Gardening is out of the question for us, unless the rain  slackens off. 
And I don't think I shall take the dog for another walk........
There is thunder in the  air......and she is jittery.
She will not want to go out.