Always read the fine print.
Update: Facebook has identified two issues behind the battery drain, the company announced, and said it has solved the problem with an update.
Not all iPhone users realize that, depending on how your phone is configured, Facebook can track your location at any time—and it's likely draining your battery.
It's not surprising that Facebook does this, since the company has a history of tracking users when they're not aware, and that the app can track you when it's off is clearly stated in the app itself. But the question of why the app drains your battery started as a real mystery.
On Thursday, Circa co-founder Matt Gilligan wrote on Medium that the Facebook app on his iPhone was running in the background, even when he turned off background refresh for the app, which is supposed to shut off most app functions. The app accounted for 15 percent of his battery drain as a result.
As for what the app is actually doing while running in the background, nobody was certain, and Facebook wasn't saying anything except for that it was hoping to find a fix.
Security researcher Jonathan Zdziarski analyzed the Facebook app's code and found that the app is sending devices' location information to Facebook in the background. "If you move around a lot," Zdziarski wrote me in an email, "you're likely to use more battery but the combination of GPS and networking going on in the background is likely the majority cause of battery drain."
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This shouldn't be surprising to anybody who bothered to read the fine print. Facebook's in-app location settings clearly state that if you have location history and access set to "always," then Facebook "will build a history of our precise location, even when you're not using the app."
The reason why background refresh won't stop the tracking, a Facebook representative told me over email, is that background refresh governs content updating—when it's turned on, your feed will constantly be populated with content even when you're not using the app. Location, on the other hand, is controlled by your location settings.
"We are not tracking background location if the location setting is off on your device or in the app," the spokesperson wrote me. As for what Facebook is trying to fix, if all is indeed working according to plan here, the company spokesperson wrote that the Facebook is looking into the battery issues.
"It's at best just another example of bad software engineering in the App Store, and Apple's lax approach to reviewing apps for mega partners," Zdziarski wrote. "I don't see any evidence that anything is going on here to violate user privacy."
So, there you have it: Facebook is contributing to the never-ending battle to keep your phone charged, and it's because the app is constantly tracking your location. However, this only happens if your location settings are set to "always," and this is clearly stated in the app itself.
Still, the idea of Facebook tracking you everywhere is bound to be an unsettling one for the more privacy-conscious, and thankfully there's an easy solution: turn your location settings off for Facebook.
Update, Oct.17: A Facebook spokesperson emailed over the weekend to say that the battery drain issue "is not caused by improper background location collection," and that the team continues to investigate the issue. "We are not collecting background location on iOS unless Location Access is set to Always on your device and you have enabled Location History in the Facebook app," the spokesperson continued, reiterating a previous update provided on Friday. The lede has been updated to reflect this.