I made one of these for my wife- http://www.instructables.com/id/How-...harger-simple/ Only took an hour (mostly spent trying to find the soldering iron which I had left in the trunk of the car while fixing the trailer brake lights) and it generates a enough juice to keep her G1 charged while driving. The box is small enough to mount on your fender, rack or whatever. There are commercial ones as well but I know I can keep this one going indefinitely and it was dirt cheap.