Battery problems with a21m

[Luda]

I have an odd problem with my battery, well not really the battery but with windows recongnising the power left in it. when i start the machine on DC power with 100% charge it shows about 2 hours left. it will randomly drop to 0 minutes or upwards of 10 minutes left. i can use it for around an hour til it actually dies.

this is a reformated machine, with nothing from IBM, are there any special drivers i should have other then the ones that come with windows XP?

P.S. the battery is showing empty in both the windows gauges and the NHC gauges.