Many computers have a Cmos battery (even an Xbox has one of these but that is rechargeable) and when they fail you have to get a new one.
At least a bad battery is better than a failed motherboard, LCD, etc.
I bought 2 Pavilion ze4908 notebooks for Christmas. The one notebook does not keep time. Spoke to HP in India today and took me through a few tests. I have to return the notebook to HP now. They say the battery failed. Is this normal with batteries or with HP?