Here is the one thing that you need to do right now! Turn-off background app refresh for Facebook.
Settings / General / Background App Refresh - Turn off Facebook.
While you are in there, go ahead and turn off any other app that you don't thing you need background app refresh turned on for.
What is background app refresh?
When Background App Refresh is on, apps can refresh themselves in the background. For example, an app can check if new content is available and download the updates, or retrieve the updated content in the background when it receives a push notification, so the new content is ready for viewing when you launch the app.
With this simple change, you will see a noticeable increase in your battery life.