The battery health drop quickly I don’t know if it’s the battery r the phone

Which exact iPhone model do you have? Is the battery the original one that came with this phone or is it a replacement? If it is a replacement, was it done by Apple, or some other 3rd party?

The support article you came here from provides you with information on what you can expect for battery performance with an iPhone 11 or newer model. Did you review it yet?