Battery health new iPhone

On June 2nd I received my brand new iPhone XS. I’ve been very careful with the battery usage and charging, since that was a big issue on my old iPhone (a 7). I don’t keep the charger plugged when the battery has reached 100% and hardly watch YouTube videos/play games so that I don’t have to charge as often. Yet still when I check the battery health it’s already (June 14th) on 98%. I asked a friend who’s had an iPhone 11 since like March what her battery health was, and it was still on 100%. She charges it overnight, watches YouTube videos and plays games on Snapchat. The only thing I could possibly think of could be the culprit is the fact I sometimes use a third-party charger. I don’t know if that has any influence on battery health? I hope someone can help me figure this out! :) thanks in advance.

Anne