i don't think its battey its self but the update was for battery and camera I think the battery is telling the phone its dead when its not it will turn on when I plug in and stay on until I go into camera and then wont turn back on until I plug it in iwas told to flash it back to android 4.3 but I don't know how
Your problem is exactly like my problem.
I spoke with an engineer technicians Mobile!
Nfc and the rest of your old device and then he say firmware update, or flash custom kernel looking into the firmware itself could have some!
Or wait for Sony to be updated!
So tell me, but also my previous version was 4.3!
i probably bug in rom!!!
I think it's not bad, we reported Sony or Mr. @DooMLoRD