Understand that this worked for me, I am not saying that this will work for you.
I was suffering from a huge battery drain, I noticed that it was coming from "Exchange Services" (I have an Exchange account on the default Email App, specifically an Outlook.com account). The Exchange services were keeping my phone awake all the time and using wifi/mobile data.
What I did was disable Tasks syncronization (I kept email, calendar and contacts synchronization active). Then I changed my syncronization interval from automatic (push) to manual, this did Exchange to stop any data activity, after this I changed back the syncronization interval to automatic (push) again.
So the problem I found is that Exchange services couldn't syncronize any Tasks, it was just trying... and trying... while this my phone was being awake, downloading a lot of data (almost 1MB per minute) and draining my battery (1% every 2~3minutes).
So if you're having battery drain and uses an Exchange account on your phone, you won't get hurt for trying this :P