Last week, Apple published a support article on its Chinese website outlining the technical reasons behind a spate of iPhone 6s devices that have recently suffered severe battery problems.
The problems, which seemed to arise not long after the release of iOS 10, turned out to be a physical battery problem, with Apple clarifying that affected units having been "exposed to controlled ambient air" for longer than they should have been.
Acknowledging the problem, Apple launched a free repair program last month for 'a very small number' of affected devices. Specifically, it's devices with serial numbers that contain these characters in their 4th and 5th position; Q4, Q5, Q6, Q7, Q8, Q9, QC, QD, QF, QG, QH (thanks to ariusbb for pointing out the affected range via comments on our previous coverage).
However, Apple published an update to the support article today, this time stating that it is investigating phones with issues outside of the previously reported range;
"A small number of customers outside of the affected range have also reported an unexpected shutdown. "
The statement goes on to say that Apple will update its diagnostic tools via an iOS update to be released next week, which is likely to be the public version of iOS 10.2;
"In an effort to gather more information, we are including additional diagnostic capability in an iOS software update which will be available next week. This will allow us to gather information over the coming weeks which may potentially help us improve the algorithms used to manage battery performance and shutdown."
When logging a support call with Apple for iOS devices, an Apple representative can activate specific diagnostic tools on an affected device (with the owner's permission) and collect the subsequently created logs.
It's possible that due to large numbers of complaints from customers outside of the affected range, Apple is looking at the possibility of a wider battery problem, or that a software or firmware update has adversely impacted the battery life or charging routine of some devices.