Mobile shut down with 50% Charge while using internet

[Jadu]

I just updated my Sony xperia z1 to lollypop version..
After updated the phone I didnt find any problem at all.
But after 3 months of updated I am facing a big problem.
While I am using my phone with Internet it shut down when its charge about 40-50%. Without Internet its also shut down but after 20% of charge remaing.
I am using the orginal Sony charger.
What should I do now? Plz help

[Uliwooly]

@Jadu

That's rather odd, repair the phone with PCC and report back

software repair

PC Companion (PCC)

Bridge (for Mac)

Alternatives on How to backup Xperias

http://talk.sonymobile.com/thread/36355

[FrontierGate]

I think your battery is dying. How long have you used the phone in terms of battery recharge cycle?