I cam from the 7 Plus and can't find battery %.....is it not on the XS Max because of the notch?Your battery meter requires calibration. You usually won't see it on a day-to-day basis, but a first charge will be more dramatic than others. You don't need to do anything. Just let it sit and charge, it will eventually start moving. what is "0%" and "100%" will change over time, and your phone is just figuring that out on the first charge.
Give it up to 4 hours before starting to worry. 6 if you're using apple's slow charger.