You may know it, after some updates, your iPhone is slower and slower. In 2017 and 2018, authors of benchmark tool Geekbench discovered, that older iPhones got worse performance on newer iOS versions. Someone may think that it’s because Apple wants to sell more iPhones, but Apple said that it downgraded performance because of older batteries, which got not enough power to support iPhones and Apple wanted to prevent random restarts. Questionable is, that Apple did not say it, so there is possible that Apple wanted to sell new iPhones instead of just new batteries.
Apple agreed with voluntary settlement. Apple must pay from 310 up to 500 millions of dollars. This agreement must be appproved by court.
If you are US resident and you own iPhone 6, iPhone 6 Plus, iPhone 6s, iPhone 6s Plus, iPhone 7, iPhone 7 Plus or iPhone SE, and if you used iOS versions 10.2.1 or 11.2 before December 21, 2017, you will get about 25 dollars, based on how many owners of mentioned smartphones will apply.
In newer iOS versions, you can look for health of your battery. Just go to Settings app and then Battery -> Battery Health and check “Maximum Capacity”. Also, there is said if your iPhone supports peak performance.