I commute via bicycle, and my truck has a farad capacitor on the stereo which has quite a parasitic drain on the battery.  So after getting tired of constantly having to jump the truck every time I wanted to drive, I got this unit and mounted it beside the battery.  Works great, battery is always charged.  I just wish the cord were longer so I could plug it in without having to raise the hood.  I'm trying to find a nice short extension cord for this purpose...