Battery health drops by 4% in a week

My iPhone 11 battery health dropped by a staggering 4% last week from 96% - 92% all in the space of 5 days which doesn’t seem normal to me because I bought my iPhone in December last year and the battery health has dropped by 8% in 6 months. Mind you my sisters iPhone 11 is at 85% and she’s had it for 2 years. Is it normal that my battery health has depleted so fast in six months?

I used a 20 watts type-c adapter and recently updated to iOS 15.5.