I dont believe I ever seen battery percentage go back up so it will only go down from 98%. This is normal so nothing to worry about it. My Xs Max in one year of usage went from 100 to 91% and my 11 Pro Max is currently at 98% from 10 months usage, all batteries produced are not exactly the same so everyone may get different percentages but as long as you are over 80+% battery percentage the iPhone will still work as intended.