Lift the front cover of the thermostat upward.
Push the battery release latch inward and upward to remove the battery housing unit cover. Press the battery release lever downward. The batteries will pop out of the thermostat.
Insert two AA 1.5-volt batteries. Follow the +/- directions on the battery housing unit for proper placement.
Slide the battery housing unit cover over the batteries and back into position. Lower the front cover of the thermostat unit.