Hi there
Yes exactly i heard about it, but don’t worry, it will be ok on the next update. iOS 11.4 and so. Yo should maybe wait about at least a month for this version of iOS, i think this bug or problem will be certainly solved.
And look, that’s not something too bad! You know that your device has a good battery performance which support peak voltage. No unexpected shut downs, Your device isn't slow, so that’s perfect!
I’m using iPhone X, battery health was 97% a few days ago. in the setting and the “Battery Health” app. After that it became to 95% in both setting and the app, I let it drain to zero and fully charged it again to 100% percent and let it connected to the charger for several minutes. The battery health app now has become to 99%! I try to measure it several times in several days and Yes, it’s really 99% again and again! But setting still says 95%! Its really immutable, I don’t know why