A former Apple, ahem, Genius, claims to have devoted "years" of his life to solving the issue of poor battery life on iOS devices, a problem that appeared to become more widespread with the arrival of iOS 7.1. His hypothesis? It's mostly Facebook's fault.
In an exhaustive story over on Overthought, the ex-Apple man claims he was seeing Facebook routinely pop up in battery power tests, even when the app wasn't running. It seems to be able to permanently plug itself into the OS, with the tester noting that: "Facebook kept jumping up on the process list even though I wasn't using it. So I tried disabling Location Services and Background App Refresh for Facebook, and you'll never guess what happened: my battery percentage increased. It jumped from 12% to 17%. Crazy."