iPhone 15 Pro Max - Battery Health
How to improve your battery health on iPhone 15 pro max
iPhone 15 Pro Max, iOS 17
you can't ever, as with all rechargeable batteries you can only delay their demise and when their demise comes about you can get it replaced.
have you read
About the battery and performance of iPhone 11 and later - Apple Support
and maybe iPhone Battery and Performance - Apple Support
and Batteries - Maximizing Performance - Apple
people report apple does not change the batteries until they are lower than 80% in health