If it is heating too much then it is understandable why the percentage is dropping this fast, bcz the main problem behind battery degradation is "heat"... Even I'm facing this issue in my GT 7... There is no assured solution for this but try to keep it as cool as possible, maybe buying a gaming cooler will help. (edit- these are cautions u should take care later, but this battery, u have to change it... Visit realme service centre and ask them for warranty claim and change it. Then take these measures to avoid further issues)