most smart battery chargers have a "supply" function which is ideal for this, I use my c-tek to power up the 750 when I want to work with it inside. The main issue is you need the garmin plug so either have to unwire it from the boat or get a new plug / lead ( or make one up if you can get the plug on its own)
Yep the free map source is as good as option as homeport....so they are not making map source any longer? Plenty of blokes will have it on disk though.