Compaq Armada 7800 will not start with battery

I have a Compaq Armada 7800. With the power cord connected the laptop runs
fine and power management reports only 3% of the battery is full and that it
is still charging when in fact its not. I have a new battery and external
charger so I know the battery is good and fully charged, also the laptop
will charge the battery with no problem too. Its when I try to power up the
laptop with the just the battery, the laptop will boot and I see the Compaq
screen then the laptop will shut off and will not power up again until I
remove the battery and slide it back in the laptop will power up again and
shut off everytime at the Compaq screen. I have tried both bays with the new
battery just to get the same end result.

Is the problem in the system board or could it be the power supply. Thanks
for any help...