Apple is giving customers a US$50 credit to all customers that bought an out-of-warranty iPhone 6 battery replacement. To be eligible, you had to have bought it between January 1, 2017 and December 28, 2018.
iPhone 6 Battery Credit
This is an extension of Apple’s US$29 battery replacement program. This program went into effect December 2017 to give a cheap battery replacement to customers affected by iPhone throttling.
The credit will be provided as an electronic funds transfer or a credit on your credit card used to pay for the iPhone 6 battery replacement. Also, the replacement had to have been done at an Apple Store, Apple Repair Center, or Apple Authorized Service Provider.
If you’re eligible, Apple will send you an email between May 23, 2018 and July 27, 2018 with instructions. If you haven’t gotten an email by August 1, 2018, but believe you are eligible, contact Apple by December 31, 2018. Proof of service at an Apple authorized service location is required.