My Garmin GPS runs either on six AA batteries or a plug-in to a car's cigarette lighter. Rather than unning down the NiMHs, I'd like to work with the GPS at home using an independent power supply. I have a 6/12 volt battery charger that charges at a 1amp rate and a stand alone socket that can accept the car plug. Is this risky? BTW-would it be more risky to run with the charger or with a leftover AC power supply that's rated as 12V, 300 mA and actually tests at 15-16v?