Why my iPhone XS Max's battery percentage is dropping quickly?

Hi , I’m using iphone xs Max

it’s nice but please clear my one question my phones battery drop 4% in one month I purchased it on 82% today 17 April it’s 1 month i have experiencing iphone Xs max it’s 79% service. why my phone batter drop 4% in one month.

my daily usage is 6 hours approx.

and using charger Type C to lightning 25 w

[Re-Titled by Moderator]