I get that all the time. If you put it on charge (plug the cable in when the Android boot screen comes up) once it is fully charged NITDroid will recognise the battery is fully charged, if the battery is almost full to start with this will only take a few minutes. I would love a better solution though, since it makes NITDroid a pain in the arse for me to use as I just want to pop in a fresh battery and use it without having to go through this rigmarole of getting NITDroid to recognise the battery really is fully charged.