In an effort to fix a “very small number” of certain iPhone 6S models that have been unexpectedly shutting down, Apple is offering a free battery replacement for the phones that have been manufactured between September and October of last year.
If you think that your phone or someone else’s phone has been affected by the issue, you will first need to check for a corresponding serial number on the device at an Apple Store or an Apple-authorized service provider. It is important to note that carriers selling the phone won’t be replacing the battery.
Just a reminder, before you go into the Apple store to replace the battery, Apple is advising you to back up their data, erase the settings and turn off Find my iPhone. Also according to Apple, they will not be replacing cracked screens. And any unexpected shutdowns on devices manufactured before or after the set window will not get you a free battery replacement, either.
And also, if you have paid for a replacement battery between the September and October 2015 timeframe, you will be able to get a refund for the purchase.