I bought my Lumia in the first week of Jan 2014. It worked well for the first 6-7 weeks. However, towards the beginning of March, I noticed heavy battery drain and the phone was heating up like crazy (it was getting so hot that I couldn't even carry it in my jeans/trouser pockets!). Even when the phone was left untouched, it was draining 7-9% per hour ! For the life of me, I couldn't figure out why. When I took it to an authorized Nokia center (here in London), the guy was going on & on about how I had so many email accounts (5 Gmail + 1 Outlook.com account), FB, Twitter, Instagram, etc. and he told me that I shouldn't be surprised about the battery drain. I told him the phone had worked well for the first couple of months, but that fell on deaf ears. He basically thought I was some dumb dude who didn't get even the 'T' in technology ! What a bozo.
Exasperated, I turned to online forums (again). In one of them (not able to find the link to that article now), someone (bless his/her soul) suggested that the drain may not be because of GMAIL sync (remember, I have 5 GMAIL accounts and no problems initially) but in particular, it was Google Calendar. That user suggested to change the sync server for Google Calendar from the default "apidata.googleusercontent.com" to just "www.google.com". I did that last week, and voila, my battery life is now back to what it was when I got the phone i.e. the battery drain of is just 1-2% per hour on idle which I'm more than happy with.
Hope this helps. :smile: