I ran across some cool solar cells and built a HV charger for the pack. Have not tried it out on the car yet. As configured, it only charges with 85MA, so it would only be good for a top off charge. The low current should keep any overcharge from doing much damage?
Info about the cells and panel are at:
http://www.99mpg.com/mikestips/
Don't try this unless you know what you are doing. The panel can give you a good shock, and under certain conditions even kill you. Put enough 9V batteries in a series string, and you have the same condition.
Don't let YOUR magic smoke out.