Battery drained 1% with in a 2months span time

my iphone 12mini buyed on oct-12th.

within 2months battery degraded 1% why i dont know ? Daily i am charging only 1 time but degraded 1% shocked.

charging time mobile is heating.

help me to sort out of this problem

i am using polycarbonate back case.

if we use back case battery will degrade are not ?