Join Date: Sep 2005
Bikes: Windsor Fens, Giant Seek 0 (2014, Alfine 8 + discs)
Overcharging should not be a problem. You're hooking one SLA battery in (EDIT)parallel with another lead acid battery (the car battery). If it's good for one, it should be good for the other.
EDIT: NOTE my caveat below; you'll want to have a resistor in the circuit
Lead acid cells are very difficult to overcharge.
In fact, most jumper pack batteries, which are just SLAs in a nice plastic box, come with a charger lead which is just two cigarette lighter plugs on a wire, intended to do exactly this.
Work: the 8 hours that separates bike rides.
Last edited by ItsJustMe; 05-24-10 at 07:46 AM.