Casio Protrek watches are generally solar powered. However, they all come equipped with one single battery to power the watch should the solar power fail. In general, these batteries do not have to be replaced. Casio guarantees them to last as long as the watch itself does. There are times, however, when the battery does fail. In those few cases, it is required of the owner to replace that single watch battery. A replacement battery can be bought at the local department store.
Use a pin to compress the two pins required to remove the band on the watch and remove the band, as the band prevents the back from being removed.
Use the Phillips head screw driver to remove the 4 screws from the back of the watch.
Remove the back of the watch. It should be pried off gently.
Remove the rubber sheet that is covering the battery cover.
Press the pin into the noon position on the battery cover. This will release the cover.
Slide the battery out.
Place the new battery in the battery cavity and replace the battery cover and rubber shield.
Place the back of the watch in place. With the Phillips head screw driver screw each of the four screws back on. Make sure the screws are tight enough to hold the back into place but not excessively tight so that the screws become stripped.
Reattach the watch by inserting the two pins into place.