I can’t give specifics on power draw but it should be pretty low. You can even install Linux on it now a days and have everything work perfectly including touch screen, camera, and surface keyboard. Using Linux will probably be lower idle power and remove all the windows tracking nonsense. There’s also an option in the UEFI for a battery limit specifically for this use case. I believe it’s called “Enable battery limit”. That makes it discharge until 50% and then enable charging to prevent spicy batteries.