Thought I would post an update on my battery life experience. For me, something within the Facebook app and the Facebook Messenger really kills my battery. I installed after a factory reset, and everything was fine for about a week before the battery started getting progressively worse. Facebook Messenger showed up as the culprit, so I uninstalled that and battery life got substantially better; not as good as under a fresh install but still much better. After a few more weeks, the battery life again got progressively worse; reboots would partially stop the drain, but it was not perfect. Suspecting something within Facebook's code, I uninstalled the main Facebook app, rebooted the phone to recovery, wiped cache, and rebooted again. Battery life was back to normal - after a day to test, I then re-installed Facebook, selecting it to sync existing contacts only (not events or pictures), and battery life back to normal (which for me is about 16 hours with 2 hrs of on-screen time). I just reinstalled Facebook Messenger and will see if the battery life is still OK.
Odd thing is that Facebook App never showed up as a high use of battery in the battery settings or GSAM. Facebook Messenger does, however.