Have you noticed an unusual battery drain on your iPhone or iPad lately? German iOS developer Sebastian Düvel has, and he decided to get to the bottom of it. He used Apple's Instruments OS X app, which allows developers to analyze and test iOS code, and found that Facebook's apps were the root of his battery drain problem.
In short, Düvel discovered that Facebook's apps are not shutting off like they should when they are in the background and not in use. Düvel found that the main Facebook app would become active for about 10 seconds and then go back into a sleep mode before becoming active for another 10 seconds again -- this happens continuously, all day long. The same thing happens with Facebook's Messenger app.
The way iOS apps are supposed to work is when they are not in the foreground -- that is actively being used by the user -- they go to sleep and are not active again until the user brings them forward. Facebook's apps do not do this, and are activating in the background, thus draining battery life.
Apple's rules require that most apps do not actively run in the background. However, it does make exception for some apps, most notably audio apps like Spotify and Pandora that play music in the background when you're in another app; location-based navigation apps like TomTom; and VoIP apps like Skype.
Facebook actually meets the criteria of an audio app and a VoIP app, so it's not breaking any of Apple's rules -- but as such, Facebook's apps could be eating through your battery life. Düvel says his aim in publicizing the battery drain Facebook's apps put on your iPhone was not to embarrass the company, but so that hopefully they can fix the problem in their code so the apps don't activate as much in the background and thus can save the user battery life.