Apple has been forced to admit that a battery shutdown issue plaguing iPhone 6S users is more widespread than it initially thought.
Apple first admitted to the problem, which it said has caused a "small number" of iPhone 6S handsets to unexpectedly shutdown, last month.
At the same time, the firm launched a battery replacement programme, allowing those with a borked iPhone 6S to get a new battery fitted for free.
This week the firm has confessed that the issue is affecting more iPhone users than initially thought, admitting that it has spotted similar problems with devices that were manufactured outside the original September and October 2015 timeframe.
It's also revealed what it believes is causing the problem, blaming the battery shutdown on "ambient air".
"We found that a small number of iPhone 6S devices made in September and October 2015 contained a battery component that was exposed to controlled ambient air longer than it should have been before being assembled into battery packs," the firm said in a post on its Chinese website.
"A small number of customers outside of the affected range have also reported an unexpected shutdown. Some of these shutdowns can occur under normal conditions in order for the iPhone to protect its electronics."
Apple has said that, alongside its battery replacement programme, it is preparing a diagnostic tool to gather more information and figure out if it can be resolved with a forthcoming iOS update.
"In an effort to gather more information, we are including additional diagnostic capability in an iOS software update which will be available next week," it said.
"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. If such improvements can be made, they will be delivered in future software updates."
Before announcing its worldwide battery replacement program for the iPhone 6S, Apple was also forced to admit that some iPhone 6 Plus handsets had been experiencing display glitches, better known as 'Touch Disease.'
While it'll replace iPhone 6S batteries for free, Apple has told iPhone 6 Plus users that they'll have to pay $149 (around £117) to get the issue fixed. µ
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