any problems you are facing

netwrok issue.

buddy those days are gone now.. if you want to caculate your performance of battery then there is no harm in charging it from 0 to 100

Apply for One UI 2.0

No. See you have charged in between.. its better you drain it out completely and charge it back to 100% and then use it in normal way and let us know the screenshot. We will be able to help you accordingly