Apple has acknowledged that there are battery problems on some iPhone 6S models that cause the devices to unexpectedly shut down. In a statement posted by Power Mac Center (the authorize partner and service center of Apple Inc.) in their Facebook and Twitter page, they said that the iPhone 6s Battery Replacement Program is now available in their service center.
The Apple iPhone 6s Battery Replacement Program is now available in our Service Centers.
A very small number of iPhone 6s devices have been determined by Apple to unexpectedly shut down. This is not a safety issue and only affects devices within a limited serial number range that were manufactured between September and October 2015. If you have experienced the same issue, you may email our Customer Service Team through [email protected] or call (02)725-4PMC (4762) for further assistance.
You may check if your iPhone is eligible by visiting this link 10.