Battery Health Dropped ?

Hi, I bought my iPhone 13 pro max less than a year with of course 100% battery health. And after few months using it, my battery health keep dropping?? which now it’s at 95% . I don’t understand why? What did I do wrong? Before this I’m only using iPhone 6 and the battery health was only dropped to 90% after like 5 years of using it. Why this happened to my iPhone 13 pro max tho?