Battery Health

I have had my iPhone 12 Pro Max for less than two months now. It will last me all day long no problem. When I go to sleep at night I plug it in, it’s set for optimized battery charging. I get up around the same time and it’s fully charged. The problem is, in less than two months my battery health has dropped to 96%. My wife got her iPhone 11 shortly before mine, has almost the same usage and charging habits, and her battery health is still at 100% Why could mine be going down so quickly?