Battery Health Issue.

Hey, I have bought an Iphone 11 pro on June1,021. And within 2 months it dropped the the battery health from 97% to 96% mean, only 1% but I really do not understand why this happened. Even though, I do not charge it on daily basis but it is my first experience with IOS. If someone knows that why did this happen then pls let me know. Its giving me trauma.