I recently changed the battery
There is a 437 stamped into the back of the case for one of the two versions (437 and 438) of Casio WR watches, with the 437 being the kind with raised rubbery number buttons. The model no. for the 437, also on the back case is CA-53W, useful for ordering parts (see below). These instructions are for the 437 but should be useful in many cases for other Casio watches, with numbers other than 437 or 438 on the back of the case. For example, the resetting process described in step 5 below appears to be common to many if not all Casio watches. There is no manual on the casio.com website for many watches, including the 437 and 438. There are no instructions for changing the watch battery in the manual for the 437 or 438 either, nor for many if not all Casio watches. If there is a 438 stamped on the back of the case, the chip is the same as on the 437. The buttons on the face of the 438 watch are flat plastic rather than raised and rubbery. The two buttons near the top serve the same function on the 438 watch as the right side buttons on the 437. The left top button on the 438 corresponds to the top right side of case nonindented button on the 437. The right top button on the 438 corresponds to the bottom right side of case lower indented button on the 437. Save time and money by replacing the battery yourself If you send your Casio watch off to have the battery replaced, it will likely cost you about $30 USD. Many jewelers will routinely send a Casio watch off for battery replacement rather than replace the battery themselves, so these instructions may help save you from delays and expense if you do it yourself. Likewise, jewelers may find these instructions useful for satisfying customers by replacing the battery on the spot rather than having to send the watch off to Casio. Materials needed a. 5/64" Phillips head screwdriver (A set of different size screwdrivers in a small black plastic case, including the 5/64" was bought for $1 USD at a local Dollar Tree store in the USA.) b. Watch battery identically numbered to the dead battery on the watch (2016 on 437 case back number) c. Metal tweezers to reset the watch d. Sil glyde gel grease or any other grease, to maintain water resistance f. Toothpick or similar to spread grease in O ring slot g. Ziplock plastic bag or bowl to hold the 4 small screws so they don't get lost Instructions on replacing the battery and resetting the watch 1. Take off 4 back screws, using the 5/64" Phillips head screwdriver. One screw was balky and needed to have the screwdriver handle attached to a vise grip pliars, with the watch held in the other hand and rotated. Putting the screwdriver handle in a vise would also work to stabilize the screwdriver, while turning the watch held in one hand. Set the 4 small screws aside in a ziplock bag or bowl. 2. Remove the red cellophane cover on the battery, held by two tabs cut into the cellophane fitting into a slot on the metal hold down battery strap atop the battery. 3. With a fingernail or toothpick (nothing metal), slide the battery to the side, out from under the metal hold down strap atop the battery. 4. Insert new battery with fingers/fingernails, sliding it into place from the side. The side, with the battery number showing (2016 on 437 case back number) faces outward, just as on the removed battery before it came out. The watch will continue to appear dead, with nothing showing on the display until the electronics are reset in step 5. 5. Reset the electronics by using a pair of metal tweezers to simultaneously touch with metal, the outward facing side of the battery, and the brass terminal in an indentation in the plastic about 4 o'clock and about 1/8" outside the battery diameter. To aid in orientation, there is a barely visible small AC (presumably meaning "all clear") pressed into the metal near the battery and the indented brass terminal at about 4 o'clock. It may be necessary to tilt the watch in the light so the light strikes the AC so it becomes visible. Verify the display is working. Resetting the time will be in step 11. 6. Reinsert the red cellophane cover removed in step 2. It may be necessary to slide a knife or similar between the strap holding the battery down, and the battery, to make room for the two cellophane tabs to be inserted in a small air space between the strap and the battery. (When installed, the cellophane tabs do not prevent current from flowing between the top of the battery and the battery hold down strap.) If you use a knife or other metallic object to open up the strap to battery space to allow entrance of the cellophane tabs, take care not to short the battery against metal parts of the watch other than the hold down strap. Quickly glance to see make sure the display is still working after the cellophane is back in place. If display not working, repeat steps 2, 5 and 6 (remove cellophane, reset watch, reinstall cellophane). 7. Remove the rectangular O ring from the case back removed in step 1, or the case, and coat it with Sil Glyde silicone gel grease or similar, to retain water resistance. White grease or any grease should also work. Set the coated O ring on the inside of the metal case back removed in step 1. The O ring will eventually mate back with the O ring slot in the plastic case. 8. Using a toothpick or similar, coat the rectangular O ring slot in the plastic case with the same grease used to coat the O ring in the metal case back, to provide extra water resistance. Grease is nonconductive, so there should be no damage from shorting if some of the grease gets inside the watch. 9. Wipe hands clean and wash hands and/or use plastic gloves to avoid putting too much grease on the outside of the watch. 10. Replace case back removed in step 1. Screw in the 4 removed screws with your 5/64" Phillips head screwdriver.