The hekate trick mentioned above probably won't work. At least it didn't for me. When the battery indicator has a strange behaviour like that, the only thing that worked for me, was to let the battery completely drain, and I mean, absolute zero power. You shouldn't get anything when you press the power button. Then plugging the charger directly, the screen turns on with the battery indicator on the top left corner, and stays on for about ten minutes, then finally turns off. It should then charge normally and the battery indicator should be OK from then on. You will lose the system settings and time/date with this technique, but it's worth it to get back a precise battery indicator.