Z3 battery draining quickly

[SuxXarD]

Hello,

I've had my Z3 for approx. 6mo now. 

Everything worked great up until recently. 

I'll have a full 100% battery, and after maybe 10-15 minutes, it drops well below 70%. 

This is with it sitting on my desk, screen locked etc. 

Over the passed week, the issue has gotten worse; it will drop from 70-80% to under 15 in a matter of seconds. 

I've gone all over Google looking for solutions, but can't come up with a remedy. 

I've power cycled, restarted, tried booting to safe mode (which it doesn't want to actually do), and all of the various other diagnostics I've come across. I've even powered offby using the little yellow tab under the sim/micro usb panel. 

The kicker is, it'll randomly jump back up to 50+% randomly. 

I'm at a loss here, and don't know what else to do, shy of having to bite the bullet and buy a new phone. 

Any thoughts or input would be greatly appreciated. 

Thanks

[Qatrium]

@SuxXarD

I'd suggest that you perform a software repair using Xperia Companion. This will do a clean installation of the latest firmware and will also wipe your internal memory. Don't forget to backup using Xperia Companion, but preferably without adding apps or settings to the backup.

Follow the steps given in blue links, and keep us updated.

[SuxXarD]

@Quester

I'll give that a shot.

I've noticed that if I tap on the back of the device, near the top half, the battery will jump to 50% then immediately back to ~20%.

I'll post if the Companion doesn't help.

Thanks