Two weeks ago, Apple issued a global battery replacement program to address a problem where some iPhone 6s handsets manufactured between September and October 2015 may unexpectedly shut down (see if your phone is eligible for a free battery via Apple’s web tool).
While the company originally did not say why these devices are shutting down when the battery indicator drops below the 30 percent mark, MacRumors points us to a message posted in a support document on Apple’s website in China which blames the problem on a manufacturing issue.
The company has said that the issue is related to some batteries having been overexposed to “controlled ambient air” during the manufacturing process, causing them to “degrade faster” than usual.
Here’s Apple’s message in its entirety:
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. As a result, these batteries degrade faster than a normal battery and cause unexpected shutdowns to occur. It’s important to note, this is not a safety issue.
If your device is eligible for a free battery replacement, contact your nearest Apple retail store or an authorized service provider. Folks who have already paid to have their eligible iPhone 6s battery repaired or replaced can contact Apple Support regarding a refund.