"Apple has announced that users with devices that had service performed and paid for by the user between January 1, 2017 and December 28, 2017 will be notified by email about the refund. Eligible battery replacements must have been completed at an Apple authorized service location, meaning an Apple Store, Apple Repair Center, or an Apple Authorized Service Provider.
The credit will be provided as an electronic funds transfer or a credit on the credit card used to pay for the battery replacement service. Emails will go out starting on Wednesday through July 27, 2018 with instructions on how to obtain the credit.
Should a customer feel that they are entitled to a refund and weren't contacted by Apple, the company requests that they contact Apple before the end of the battery replacement program on Dec. 31. If contacting Apple is necessary, proof of service at an Apple authorized service location may be required...."