Apple has confirmed that a "very small percentage" of iPhone 5 devices have a battery issue that could see affected phones "suddenly experience shorter battery life or need to be charged more frequently".

The phones in question were sold between September 2012 and January 2013. 

Only phones with serial numbers in a limited range are affected, and Apple will replace eligible batteries free of charge. You can enter your serial number and check eligibility on Apple's website.

However, if the phone has an issue that could "impair the replacement of the battery", such as a cracked screen, phone owners might have to resolve the problem before the free battery replacement.

The process has been available in the US and China since last Friday, and will become available in other countries from August 29th.