Ok..so first get your phone's battery percent to 10%(or even lower) after that switch off your phone..and then charge it to 100%..do this 3-4 Times (this method fixed this same problem for me)...if it didn't work...it could be a kernel problem or something like that. So try to flash another Rom..
Sent from my ST25i using XDA Free mobile app
IF I HELPED YOU PRESS THANKS BUTTON
[DEVICE] SONY XPERIA U
[Model No.] ST25i
[Status] Rooted, BL Unlocked
[Android version] 4.0.4 (ICS)