rebuild for constant power

i need to be creative and need some help to find a solution on this.

I am think about buying a samsung S6 from a guy at work,

and i am onley going to use this i my car, will never take it out.

So need to get it power somehow, i cant use the USB, because iam going to use the usb, to the OBD in the car, so need to get it powered some other way, i will have a USB port in the glovebox, so i can take power from it to the phone.

or can i just solder some wires in the phone and use the usb port, and charging that way directly in motherbord/battery