My phone is about 9 months old and the battery health has dropped to 83% in this period.
I would like to know if I can get the battery replaced for free if I take it to the Apple service center as the phone is under warranty period.
iPhone 11, iOS 14
you can try, read some say that they will not replace batteries if the % is over 80 though
I would try contacting them
Legal - Hardware Warranties - Apple and or https://getsupport.apple.com/
To keep battery in good shape you can...
charge it before it reaches 75 percent.
charge it in a normal temp place.
don’t let it get too cold, or too hot.
draining the battery is terrible for it. (When I drained mine once, it lost 20% battery health)
Lower the brightness.
if you’re storing it for a long time, keep it at 50% battery.
Do not fully charge, or discharge.
A loss of 17% in just nine months means you rarely charged the battery.
Battery Health on the iPhone 11
