X41 Tablet funky battery charging issue

[DiGiTY]

received this X41 Tablet with a 3rd party battery that never charged and two 3rd party ac adapters. i figured the battery wouldn't charge because it was of poor quality cuz it was not original IBM and the ac adapters sucked too because it was 3rd party and prolly contributed to the battery not charging.

long story short, jumped on eBay and bought a new genuine IBM AC adapter (08K8204/08K8205) and a used genuine IBM 8 cell battery and while the battery did charge fully once since I got it (6 days now) it seems to not really hold a charge and sporadically drops charges to 20% and even lower to 0%.

any ideas what the problem is?

(running Vista Ultimate)

TIA