I had a Pentium III based HP laptop that stored the password on a chip that didn't require a battery to evade such a trick. The only fix was using the backdoor password that could be generated by using the serial number of the laptop (HP required proof of ownership, but I had dumpster dived this from their offices). The backdoor password was retrieved by wiring 50 USD to a fellow in the czech republic who had the keygen tool HP support would use.
Check HP for the service manual for your laptop. This is generally a standard goal the manual will give steps for. Usually all you need is a screwdriver of the right size and a bit of guts to pull apart bits of plastic, though I find my confidence that I'm not destroying anything is greatly enhanced when I'm following the manual and have reasonable confidence all the screws are out properly.
I had a Pentium III based HP laptop that stored the password on a chip that didn't require a battery to evade such a trick. The only fix was using the backdoor password that could be generated by using the serial number of the laptop (HP required proof of ownership, but I had dumpster dived this from their offices). The backdoor password was retrieved by wiring 50 USD to a fellow in the czech republic who had the keygen tool HP support would use.