How do I replace the lithium AAA battery on the Lyric Round?

Remove the thermostat from the sub base. If the sub base is securely connected to the wall, the face plate will disconnect if pulled straight out from the wall. Remove the current battery and replace it with a new AAA lithium battery (make sure the battery polarity matches the markings on the sub base). Reconnect the face plate to the sub base and make sure the connection is secure.