I have a Garmin Legend GPS and am exploring the idea of somehow connecting ti to the battery of my SL 900, like a car charger. It goes through AA's quick. The case is waterproof, so that's not a problem, and I can figure out a way to mount it somewhere to the hull. Any electricians out there no if this is possible, or even a good idea?
You could do that, it'd be easier/better to put a fused connection right at the battery terminals.
**MEASURE THE VOLTAGE COMING OUT OF THE CAR CHARGER**
You absolutely must do that and make sure it's 12volts. If its less, which I suspect, then you would fry the GPS hooking it straight to the battery! If it is less, there will be a step down circuit in the car charger plug which you need to tie into. Simplest way would be to visit a car parts store and buy a cigarette light plug, the female portion. Then wire that to the battery and just plug the GPS car adapter in.