Some users of the new iPhone have noticed a 10 per cent decrease in battery life each hour. The guide for the iPhone 4S says the battery should last for 200 hours.
Engineers are installing diagnostics files in affected phones to try and find the cause of the problem.
One iPhone 4S owner told the Guardian he switched off Siri and location services, but the issues persisted.
He added he received a call from a senior engineer who was reaching out to people to get data, asked questions about his phone usage and asked if he could install a diagnostics file on the phone.
Culprits have been assumed to be Siri and/or corrupted contact files, but there has been no explanation yet for the poor battery life.
If you have the iPhone 4S, have you noticed any issues with the battery life? Let us know through the comments box below or via Twitter and Facebook.
Toying between an upgrade from the iPhone 4 to the iPhone 4S? Watch our video below as we pip the smartphones head-to-head
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