Battery Capacity Dropping

I have had my iPhone 11 for ~a month now and yesterday it dropped to 99% capacity. The iPhone was bought new thus meaning it originally had 100% capacity. Is this normal to happen within a month? I am charging it ~daily from 20-80 percent per cycle via the C adapter that came with my 3rd Gen iPad Pro. I've heard that using an iPad charger is harmful and I am wondering what to do to prevent it from dropping further for another extent of time. Help would be highly appreciated!