At the end of November, Apple launched a recall program for certain iPhone 6S and 6S plus more affected by a battery problem. No health risks for users from Apple, but the affected devices may stop unexpectedly. The firm is now up on the reason for the malfunction.
Apple explains on its Chinese site they have discovered that a limited number of iPhone 6s manufactured between September and October 2015 has a battery that has been exposed too long to the ambient air before assembling the devices. These batteries degrade faster than expected, causing unplanned downtime reported by some users.
Apple has set up a verification tool based on the serial number of the device, allowing customers to see if their iPhone has or not a defective battery. If your device is concerned, the company will replace the battery free.