There is a screw that holds the battery on the back under a horse shoe shaped sticker / cover. Remove this screw and CAREFULLY pry the back off at the sides near the bottom of the door / cover. Upon removing it, there is a very small connector on a short pigtail wire. Disconnect and then reconnect. You may need a pair of tweezers. CAREFULLY restore the connector of the battery to the unit with the wires directed down as to maintain the polarization.