Apple has finally confirmed that the unexpected battery shutdowns on the iPhone 6s is caused by an inherent manufacturing issue. The company has clarified in a recent public statement that the issue is related to some batteries, which were overexposed to "controlled ambient air" during the manufacturing process and thereby making them to degrade faster than normal.
Although the iPhone maker hasn't explained why the handset would shutdown when the battery level drops below the 30% mark, folks at MacRumors have pointed to a support-document message on Apple's website in China wherein a specific bug in the manufacturing process has been blamed for the erratic battery shutdown issue.
Affected users are advised to contact the nearest Apple retail store or an authorised service provider in their locality for a free battery replacement. Those who have already paid up for the battery replacement service may apply for a refund through Apple Support.
Here are the excerpts of the message taken from Apple's support document:
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.
We also want our customers to know that an iPhone is actually designed to shut down automatically under certain conditions, such as extremely cold temperature. To an iPhone user, some of those shutdowns might seem unexpected, but they are designed to protect the device's electronics from low voltage.