I should have been more clear. I was thinking of something along the lines of a hardcase which is already common for laptops, but has a usb-c port built in and

I should have been more clear. I was thinking of something along the lines of a hardcase which is already common for laptops, but has a usb-c port built in and below the case is a large set of batteries. Think a "Mophie Case" for your laptop.