It's a reporting error, and battery degredation error at the same time. As the battery is used, it's max level drops. Don't worry about it so much until you're like going to the 80s on unplug. Then, it might be time for a new battery.
J2cool; StormDroid developer | Themer | Glitch Tester
LG Ally running StormDroid 2.0
Samsung Fascinate running AOKP Milestone 4