On second thought, this might actually be a battery issue after all. When running from an Ubuntu Live CD, the battery got drained from 100% to zero in mere 26 minutes. I'm going to test it more, by putting it to a friend's laptop (near same model, should fit) and seeing how it performs there. Still, the driver shouldn't show such confusing readings - if it gets drained in a short time, so be it, but it should still show correct life left.