Repairing your phone is a waste of time and Sony know this. I have this issue and so have many others. I have restored/updated/factory reset. I even run my device without any google account attatched and issue remained.
From all my research and reading others input who have had this issue it looks to be an issue with the power management voltage technical blah blah blah blah. In other words your battery is DEAD.
People have reported fixing the issue by replacing with 3rd party batteries but I am sure this breaks the warranty. I havent had an opportunity to send my device off but have learnt alot about what kicks this reboot loop into action so have adjusted my usage accordingly until I can send it off for Sony to fix.
I foresee this issue becoming much more widespread as devices get older I just dread that I will get this fixed then it will crap out again in a few months time.
Sony are yet to acknowledge or make a statement on this enlarging issues with dying Xperia T batteries but a quick internet serach and you start to see the scale of the issue and I am seeing a sharp increase in complaints about this issue even over the last week.
