Apple is offering a credit of 60 euros to customers who paid for a post-warranty battery replacement for the iPhone 6 or a newer device between January 1, 2017 and December 28, 2017.
The prerequisite for this is that a “qualified battery replacement” has been carried out by Apple or an authorized Apple reseller.
The credit will be made automatically to the bank account or credit card used to make the payment.
This is currently explained to those affected in a letter from Apple, as iPhone-Ticker reports.
If you have not received an email from Apple by August 1, 2018, you can contact Apple directly until the end of the year, but you should have proof of repair.