AndroidOS draining battery massively on Android 5.0
The first thing I'd look for is one app that's using an extraordinary amount of resources.

Go to settings>apps> [choose an app -- I'd start with Chrome or any other browser that you use]

Then do a "Force Stop" on the suspected app.  See if that helps.  If there are any apps that you rarely use you can keep them stopped -- so you know they aren't using any battery.

It could be a hardware problem.

Disclaimer: I'm not familiar with your phone but have used 5.0 quite a bit.