I have been keeping disposable Lithiums in my GPSs for a few years now. It's been a long time since I read the manual but I thought that it said that in the case of rechargeables, they would not charge in the device and would have to be charged in a 'real' charger. That made me think that there were diodes at work keeping the batteries from being charged if left in place but that is all conjecture at this point. I do know that I have found the unit on (noticed the screen lit up after dark) when the bike hadn't been used for several days, perhaps someone passing by turned it on for me, since then I just never worried much about shutting it off but that will have to change since losing the ability to use mobile power.
No one calls the Fire Department because they did something smart!
06 DR 650, Moose RS Holder, Handguards and Skidplate, ProTaper bars, Garmin 60CSx, Motech racks w/ 20mm Ammo cans, Renazco, TKCs summer/17" SM wheels winter 08 Scrambler, Conti Trail Attacks and BlackTiger Fork mod, 05 FSE 450, 03 KLR 250, 02 FXDX, 72 WR 250 (again), 72 SL 350 K2 (again), 72 TR6R, 06 XT 225