Battery health reduced to 91%in Just six Months of Usage of the new iPhone 12

Hi Everyone,

I am a regular user of the iPhone for the past 3 years But now I am facing a very strange issue I have purchased a new iPhone 12 64 GB in the Month of December 2020 now hardly after 6 months of using my phone battery health dropped to 91 % which is very alarming I am using the standard charger and standard cable for charging but I don't know it is a bug or some hardware issue in my phone.

I am suspecting this becz I also own one 12 pro it is battery health is absolutely fine although the phone is purchased on the same day and I am using the same adapter for charging