For years Casio has been manufacturing durable, weatherproof, solar-powered digital watches. These watches use sunlight to power a rechargeable internal battery so they can be functional for years, in almost any environment. However, it is still possible for the battery to fail or become damaged. So if you have found yourself in the position of needing to replace your Casio solar watch battery and would like to do it yourself, there is a way and it shouldn't take more than a few minutes of your time.
Turn your Casio solar watch facedown to reveal the back plastic cover that is secured in place with six small screws. Some Casio models have two screws on either side of the watch face as well.
Remove all the screws securing the back cover with your Phillips head screwdriver. Remove the screws on the side of the watch if applicable.
Remove the back plastic cover from the watch by grabbing it with your fingers at either side and lifting it up. Remove the metal plate directly under the plastic cover the same way. Then use your fingers to remove the rubber protector directly under the metal plate to reveal the metal battery compartment.
Insert the tip of your tweezers into the small hole directly under the battery compartment. The battery compartment is a circular latch in the centre of the watch that is marked "Battery." Gently push the tweezers into the hole and then lift up to release the battery cover and reveal the battery itself.
Lift the thin metal bar that holds the battery in place with the tip of your tweezers and remove the battery from the compartment.
Slide the new battery (available at any electronics store or online) into the compartment and place the metal bar over it. Replace the battery cover and reassemble your Casio solar watch in the reverse order you took it apart.