This is a good way to do it. Find whatever fuse powers the seats and have some wires ready to go. That way you can connect the battery to the pins in the fuse block. As long as the wires in the car are still intact, that battery should power up the seat and you will be able to move it around.
That's how I used to test electronics at the yard. Just find the fuse and put power in there and check on whatever. Radio, cluster, ect...