I bought a variable output car plug at Wally World a couple of years ao.... use it to charge the batteries after a long night in the car.... it has adjustments from 3 to 12 volts and is 1000 mah.... I noticed this morning, when picking up a couple of wall warts, that Rat Shack has something like this now as well... although the 12 vdc output might not seem to hurt your batteries, that voltage will prematurely age your batteries and they will burst when you least expect it! I use NiMH batteries now and have had fewer problems with the car charger than with the nicads.... but still try to use the car charger only as a last resort.....