Remove the batteries from the dock by pushing the tab at the bottom of the dock in the direction of the arrow and lift straight up. Replace with two AAA batteries in the correct direction (+/-) and close the lid.
To charge the thermometer simply place it securely in its dock (it will click in). No lights are on when charging in the dock.
One hour of charging will get you up to 25 hours of use time and a 30 minute charge will yield about 15 hours of use. Ensure the batteries in the dock have power.