It's messed up, completely. I think it's the battery, but I'm not too sure. Or maybe it's the charger, and it's not really charging the battery, despite it saying so. Either way, I'll be bringing it to the local nextel store tomorrow - hopefully they'll be able to do something about it.
[ edit | looks like it's the charger that's messed up. Damn. Hope I can get a free charger... ]