The battery of my Thinkpad has a very limited capacity of about 15 minutes. So I bought a new one at eBay. To prevent memory / leakage effects, I accidentally stumbled over a diagnostic program for IBM Thinkpad T2x series. It is provided by David Jason Smith and can be downloaded here. Being the nice man I am, I set up a local mirror.

Using the program is straightforward. Just boot with the .ISO and go through the menus. There are some interesting options such as benchmarks and generic system information. Battery rundown can be found under Utility. I hope it works for you, too.