Apple is offering new batteries to owners of the iPhone 6 and above at a discounted price of $29. This is after the issues over peoples handsets being slowed down by Apple when they had a degraded battery.
Apple started offering these $29 batteries this year, but there are a lot of people who paid the full price of $79 last year for a new battery. Apple is now giving these people a $50 credit.
If you paid for a new battery on the iPhone 6, 6 Plus, SE, 6s, 6s Plus, 7, or 7 Plus between January 2017 and December 2017 you are entitled to the refund of $50.
If you have paid the full price for this battery replacement on the above devices, then you will need to contact Apple about the refund. Apple will be emailing people who are eligible between the 23rd of May and the 27th of July. If you do not get this email by the 1st of August then you need to contact Apple about the refund.
Source MacRumors