This is the proposed solution on sony mobile support forum. what do you think?
And so many others.
Solution
On Xperias with removable battery
Note the battery % . Take the battery out of your phone and re-insert it after 5 minutes or so. Switch it on and observe the battery%. See if there's any significant drop in battery % ( 5+ % or more ). Also there should be produced a gap in the battery graph, like this Battery Screenshot
Most probably this problem has been corrected.
On Xperias with built in / embedded battery
Note the battery %. Force shutdown your phone by following this key combination
Press and hold the "Power Button" and "Volume Up" for 10 seconds until your Xperia vibrates 3 times. Now switch it on and observe the battery %. See if there's any significant drop in % ( 5+ % or more ). Also there should be produced a gap in the battery graph like this Battery Screenshot . Then most probably the problem has been corrected.
If any of the above didn't help then >
Reinstall the phone's software using SUS and start fresh.
SUS >
http://www.sonymobile.com/global-en/tools/update-service/
How to avoid this error in future
This error is usually produced when the phone is left connected to the charger even after battery becomes full.So disconnect the charger as soon as the battery charging status becomes full [ ( settings > battery > full ) or ( settings > about phone > status > full) ]To help deal with it, install any app from google play that fires up any kind of alarm or notification whenever battery goes full.
Avoid using apps that monitor / manage battery, task killers, android manager, battery savers. They usually harm more than they do good.