Why are iPad and Apple Pencil battery level fluctuating?

I am facing a problem in iPad Air 5 and Apple Pencil 2nd Generation. From past few days I am noticing something strange behaviour in battery levels that after restarting iPad the battery level changes by 2-3% either it increases or decreases in iPad and Apple Pencil. For example, assume my current battery level is at 80% and 100% in iPad and Apple Pencil respectively. After restarting iPad battery level changes to 83% and 94% respectively. The change is random at every restart. Contacted Apple Support team and they are saying I should visit the Apple store for hardware check. Is this really an issue? If it is then I dont think it would be hardware issue. No issue in performance observed until now.