Read an article the other day about the amount of power the Facebook app draws from your iPhone/iPad. The nub of it was that the app can be rather busy in the background and this in turn can impact battery life. Without going into full detail of the jobs it is running in the background (some you can turn off like location, some you can't like clipboard scanning, photo scanning, etc) they did a vaguely scientific test over a week where they used Facebook via Safari instead of the app. They found batteries were on average 15% healthier if the app was not used. That's quite a chunk.
Obviously this will vary by how heavily you use Facebook but if you're struggling with battery life suggest:
- double tapping the home key
- swiping the Facebook app away
- use Facebook via Safari for a few days
- see if there's a difference to you
There's no need to delete the app, IMO, just make sure you've properly closed it, not just pushed it to the background.
I've been doing it for 3 days now and reckon there's about 10% in it and I can't say Facebook in Safari is particularly harder to use than the app itself. I am now slightly curious as to what's it doing in the background that isn't configurable to drain so much juice...
Article: http://www.theguardian.com/technology/2016/feb/08/uninstalling-facebook-app-saves-iphone-battery-life