iPhone 6s Plus won't turn on after device abuse

I was wondering if someone could assist me in trying to repair/salvage this iPhone 6s Plus that I was given to by a friend. According to him, he had repeatedly abused his device by smashing the phone's backside onto hard surfaces causing the phone to lose accelerometer & gyroscope functionality, and eventually causing it die.

The phone no longer turns on even with a hard reset, is no longer recognised by my computer and will not charge. I don't know exactly what has happened to the internals as I do not yet have the tools to take a look inside but I suspect that it has got something to do with the battery - i.e. battery dying, flex cables being disconnected from the logic board.

I also suspect that some of the internal circuitry has been damaged from repeat smashes resulting in components such as the logic board to fracture or crack. I forget to mention that the phone is also slightly warped and bent backwards, away from the display.

I would really appreciate it if someone could share their knowledge so I can at least get this phone back up and running. Ideally, I would also like to repair the accelerometer and gyroscope, but I think these involve operations requiring a high level of soldering which is arguably beyond my current capabilities. I may also look into replacing the back housing just to make the phone looking new again.