Before changing the battery of your device, please unplug the transformer.
Find the tabs at the top of the device.
Press in the tabs and pull off the cover.
Locate the battery.
Remove the wires from the battery terminals.
Attach the wires to a new battery (6VDC), ensuring the red and black wires match up with the terminals of the same colour.
Place the battery back in the slot.
Replace the cover on the base. Press in until you hear a click.
After changing the battery, plug the transformer back in and reset the clock on the device.