yes you described the issue very well . i am facing the exact same problem on my device . did you try this app
https://play.google.com/store/apps/details?id=com.ignisoft.battery.calibration
if you tried it please give me feed back .
and do you have any information about a new update or something from sony trying to solve this issue ?!
Mate, as I said; I tried every calibration method available but the issue still exists. Even though the small update provided by sony in January was supposed to address this bug, its not gone.
And frankly the app is useless. The method described by hitman1376 is the best calibration process but unfortunately the bug is in the system/rom itself and no amount of calibration can remove the bug unless a new update is provided by sony.
Regarding the update, the only thing we can do is hope and wait