Good point. I actually haven't tested it's battery life yet. It is currently not plugged into the bike. Possible that my great idea has that one flaw and I end up pulling over to check the maps on my phone again
Garmin makes a charging holder for motorcycles and it's available from the Garmin website. Works quite well with that 660. Power it up from a relay pack that runs off the tail light lead and you are good to go.