All genuine Rolex Datejust watches have an automatic or manual movement, which means they are not battery powered. Genuine Rolex Datejusts are wound when worn or by rotating the crown and manually winding the watch. If your Rolex Datejust has a battery, your Rolex is not authentic. The battery is simple to change.
Place the watch face down on a lint-free cloth, so you do not scratch the face while removing the battery. A lint-free cloth is important because you do not want any lint pieces to get inside your watch.
Examine the watch case back. If you see grooves around the outside of the removable back, you have a screw back watch. If you do not see grooves, you have a snap back watch. All genuine Rolex Datejust watches have a screw back, but replica watches could have either. To remove a snap back case, slide the tip of a small screwdriver or another flat tool in the area where the case back meets the watch case. Twist the screwdriver and the back will pop open. To remove a screw back you will need a watch case opener wrench. Adjust the prongs on the wrench to fit in three grooves around the outside of the case back, then tighten the prongs. Fit the prongs in the grooves and rotate the wrench to the left to unscrew the case back. Fully remove the case back with your fingertips.
Remove the rubber gasket around the outside of the case. You will see the gasket when the case back is open. The gasket ensures the watch case is water tight and is important to replace before you close the case.
Locate the watch battery. Remember which side of the battery is facing up. Slide the tip of your screwdriver underneath it to pop the battery out of its case. Use your tweezers or fingertips to remove the battery.
Place the new battery in the watch with the correct side facing up. Turn the watch over to make sure it is working before closing the watch case.
Put the rubber gasket around the outside of the case just as you found it when you opened the case.
Press down on the case back to close it if you have a snap back case. You will hear a "click" when the case is closed. If you have a screw back, place the case back on the watch and use your wrench to tighten it in place.