Why does my brand new iPhone 7 get hot really quick? My battery also drains a bit fast as well?

But are you playing energy intensive games?

On the matter of the battery, read this message from Apple regarding an exchange program for iPhone batteries for iPhone 6 and upwards. Your phone will qualify. https://support.apple.com/iphone/repair/battery-power

For instructions about what to do, visit this link. https://getsupport.apple.com/?caller=kbase&SG=SG003&category_id=SC0105&symptom_i d=23306

If you choose to go direct to your local Apple store, be advised to book with the genius bar as there are bound to be many others with the same thoughts. In addition to that it has become known that stock is low and many countries are waiting supplies. Due to the enormity of this operation, people will need to be patient.

The offer will be available world wide and continue until at least December 2018.

Are you playing energy intensive games and have features like brightness at full on level or locational services? If so, that is the reason.