Most iPhone users who have updated their devices to Apple's latest operating system, iOS 9, 9.0.1 and 9.0.2 must be wondering why their phone battery life dies quickly despite running on the latest firmware. Well, Facebook iOS app is draining battery of Apple handsets, including the recently released iPhone 6s and iPhone 6s Plus.

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Apple's iOS 9 was dogged by issues despite coming with several new features, but the upgraded version iOS 9.0.2 fixed almost all the bugs, including cellular data usage switch, iMessage activation, iCloud backup, screen rotation, Safari browser, Photo apps and custom APN setup. However, Facebook app continued to run in the background and reportedly eats up battery of the devices.

Facebook ideally should sleep after its app refresh is disabled but it continues to run in the background, consuming a total of 15% battery over 7 days, according to blogger Matt Galligan.

Facebook has admitted that iPhone users have complained of battery issues with their iOS app and the company is working to solve it. But no one knows the timeline and when it will be rectified.

"We have heard reports of some people experiencing battery issues with our iOS app. We're looking into this and hope to have a fix in place soon," spokesperson of Facebook told TechCrunch's Natasha Lomas. 

Users of Apple devices -- iPhone 4S, iPhone 5, iPhone 5C, iPhone 5S, iPhone 6, iPhone 6 Plus, iPhone 6s and iPhone 6s Plus – running iOS 9, 9.0.1 and 9.0.2 may face battery issue caused by Facebook app. It may come as a disappointment as iPhones are already known for their short battery life.