在「The Background Data and Battery Usage of Facebook’s iOS App」這邊提到 Facebook App 在 iOS 上使用了非常吃電的技巧來強制背景更新。
作者猜測，如果你把 Facebook App 設定成不允許背景更新，那麼 Facebook App 會利用 iOS 在「播放音樂」可以在背景執行來進行更新：(所以只是打開播放的 channel，但是沒有聲音)
My guess is that Facebook is hijacking audio sessions on iOS by keeping silent audio in the background whenever a video plays in the app. And because, by default, videos on Facebook auto-play on both Wi-Fi and Cellular and few people ever bother to turn it off, that means there's a high chance the Facebook app will always find a way to play a video, keep audio in the background, and consume energy to perform background tasks.
I'm not alone in noticing the mysterious "Facebook audio" background consumption, and video auto-play seems to me the most likely explanation at this point. I don't know if turning off auto-play may fix the problem, but I'd recommend doing that anyway to save data.
印象中我們家的 zonble 也有提過類似的事情，當時他好像還有抱怨不知道 Facebook App 在搞什麼鬼... Anyway，這就可以理解作者提到為什麼這麼吃電：
On my girlfriend's iPhone, for instance, iOS 9 reports 5 hours of on-screen usage for the last 7 days, and another 11 hours of background audio usage with Background App Refresh turned off.
我的想法是，如果不用的時候就按兩下 home 鍵把 Facebook App 整個踢出去，或者就如同作者建議用 Safari 開行動版本：
I wonder if Apple should consider additional battery controls to take action against shady practices like invisible background audio. What Facebook is doing shows a deep lack of respect for iOS users. I continue to recommend using Safari instead.