Magellan Roadmate 1212 won't stay on when unplugged

Man, I DO commiserate with you on that one, but did you specify to them that the battery should be checked?
as that is probably your problem, now that I know the unit has been checked and the worst possible outcome
from your buying an extra battery is that you will HAVE AN EXTRA BATTERY for those times when you need
total portability.

So, make sure you try a brand new battery and if that solves your problem, then buy several.