With the release of iOS 10.2.1 Apple introduced a new “feature” that would slow the processor during certain peak workloads to prevent an unexpected shutdown. The issue affected iPhones with older batteries that had begun to chimacally degrade.
This caused some negative feedback from iPhone users and Apple decided to lower the price of iPhone battery replacements for iPhone 6, iPhone 6 Plus, iPhone 6s, iPhone 6s Plus.
iOS 11 introduced the feature to iPhone 7 & iPhone 7 Plus with iOS 12 bringing it to the iPhone 8, iPhone 8 Plus and iPhone X.
The Aussie price dropped from between $80 and $119 to $39 to replace batteries on iPhones affected by the issue but the program is due to end this month so if you are affected you should get in quick!
You’ll then see the maximum battery capacity listed as a percentage and underneath the Peak Performance Capability which will tell you if you have an issue.