iPhone 6s Battery issue

Hi!

I am having issues where the battery will tell me it is at 100% and yet I have been using it for two hours. I do a reboot and then it says that the battery is at 35%. Or, I will plug the phone in and it says that it is charging but will not actually charge on the phone(ie stays at whatever percent it was when I plugged it in.) If I do a full power off and on, again it will show the right amount of battery life.

Gltichy battery? I have only had the phone about a month so I am feeling frustrated!