Have you tried it with the battery disconnected and just the power supply/charger plugged in?
See manual:
[document|1184]
page 11.
Does that fix it? Then just defective battery.
No?
Then try resetting the BIOS by taking out the coin-cell battery, page 33 in manual, and then press the power button to discharge any power in computer. Should be 3 volts. Replace if lower.
Let us know how it goes.