OK, I am a tech head and I've had this before when I upgraded my Note 2 to Ginger Bread (this problem by the way manifests on many Androids, not just samsung - going to KitKat (just search all the different forums). For me, it was 100% battery drain thanks to Exchange Services (a simple check on battery would show over 50%). I had the note for over a year given me 14+ hours usage. It dropped to about 5 hours. The problem went away if I went to manual synch on Exchange and I got 14 hours back. If that wasn't proof for me, nothing was. The fix at the time was a factory reset and a clear cache which was a pain but it fixed it. That was Ginger bread.
Now, I have exactly the same problem after upgrading to KitKat - EXACTLY. I have done a clear cache. No change. I have done a factory reset. No change. I am now running a manual synch and get my 14 hours back. What a pain though I want push exchange email.
This is SO VERY VERY annoying.... Come on Google.. Acknowledge it and fix it... Search the Nexus forums. Same problem. Search people whom have rooted phones as well. Same problem (mine is stock Verizon)....