I decided to write as someone stated:
"But the battery wouldn't stay charged, and the unit wouldn't work when plugged into the car's adapter. So: useless."
If You use Genuine Garmin charger, then there is no problem, as this is specific model, in any aftermarket charger pin4&5 of miniUSB has to be connected together, otherwise will be recognized as a PC, not charger, and unit won't work, that's why probably "feedourdogs" wasn't able use unit under charger connected