sudden shut off when on battery

[Christoph Pistor]

my good old G4 400 Mhz shoes some strange behavior when on battery. 
Suddenly while typing it shuts off. This happens usually when a key on 
the keyboard is pressed, but not a particular one. There seems to be 
some intermittent contact and I don't know where. I tried moving the 
battery to see if I can reproduce the shut off, but nothing happened.

Did anybody else have this happen? Is this a warranty case? How could I 
show this to the genius in the apple store?

Christoph