Unfortunately, I only have the User manual, not the Dealer manual for that register so I don't have the procedure to check the key assignments.
As far as the battery, yes there is a small nickel-metal hydride battery on the main board.  If you feel up to taking the cover off the register and checking it, the battery should be between 3 - 4V when the register is unplugged.  I have seen marginal batteries cause some strange symptoms, so it's hard to say for sure if it's a factor here.
                
 Steve
                
 September 2009