It was fine for the first couple months. Always accurate. Now it will show 99% battery, 18 minutes usage, I turn it off, turn off wifi, turn on 8 hours later and the usage is now showing 3.5 hours or something similar. The battery still shows 99%. I have tried rebooting but it does not help. While I am using it, it is accurate. When I turn it off for an extended period, a few hours of usage is always added. I can't figure it out. I also drained battery completely and that didn't help either.