Unless you have the phone turned off, it's still doing things even if you're not using it. Have you checked things like Settings>General>Background App refresh and made sure that it's not turned on for things you don't really need it on? What is your signal strength like? One huge drain of cellular batteries is poor signal.
Hey IOS team please work with issue on urgent basis this is happening to many IPhone users
This is a user-to-user support forum. No "iOS team" is reading here. If you want Apple to help you with the phone, use the Contact Support link at the top right of every page of these forums or make an appointment at the Genius Bar at your local Apple Store.
If your battery health is showing as 80%, it may be time for you to get a new battery.