The iPhone 4S seems to have a battery life that's far shorter than it ought to be. Some owners of the quick-draining devices reportedly have been asked by Apple to install monitoring programs on the phone to help diagnose the problem. The culprit could be a setting in iOS 5. It is most likely a bug that causes the Setting Time Zone function to keep location-tracking running constantly, said Oliver Haslam, who posted step-by-step instructions to adjust the setting and restore the device's full battery life on his blog.
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