i always having problem during charging battery to my iphone 7plus. I can feel hot on the body casing. I have to switch off the phone for a while to cool down and turn onn back the phone.

Take it into your nearest Apple store for evaluation. You will qualify for a replacement battery at a special low rate of $29 or whatever the charge is in your country. Make an appointment first.

What charger are you using? If Apple Charger which one? But, as "seventy one" mentioned, this sounds like a Hardware problem that you will not be able to solve online.