Jerry, your GPS will work fine on 6 volts I've been told. AFTER I bought & installed a 6-12v stepup so that I could run mine in the '38, a thread over on the VCCA site advised that they work just fine on 6v.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.