Power recliners have a motorized base that’s powered by an AC cord that plugs into an outlet. The motor uses a belt to drive a system of gears that push against a spring to move the recliner up and down. The gears are housed in a gear housing that’s mounted to the base of the recliner.
The electric motor powers the reclining mechanism which makes the chair go back and then when you let go of the lever it’s pulled back towards its original position by the springs.