Remove the Casio watch back to access the battery
Most Casio watches have a removable case back held on by small screws. You will need a case opener tool — a flat, thin metal tool designed to pry open watch backs without damaging the case. You can buy one for a few dollars at any watch supply retailer or online. A flathead screwdriver works in a pinch, but it is more likely to slip and scratch the watch.
Look at the back of your watch for a small slot or notch. Insert the case opener into that slot and gently twist or pry upward. The back should pop off. If it does not move after light pressure, try a different slot — some watch backs have multiple entry points. Do not force it; excessive pressure can crack the case or strip the slot.
Once the back is off, you will see the battery sitting in a metal holder, usually in the center of the watch movement. The battery is typically a small silver disc, often labeled with a code like SR626 or LR626.
Key Takeaways
- A case opener tool is the safest way to remove the watch back; a flathead screwdriver can scratch the case.
- Insert the tool into the slot on the back and twist gently — do not force it or you risk cracking the case.
- Once the back is off, note the battery type (printed on the battery itself) before you remove it.
- Most Casio batteries cost between two and five dollars and are available at pharmacies, electronics stores, and online retailers.
- After installing the new battery, test the watch before closing the case back up.
Lift the battery out of its holder
The battery sits in a metal clip or holder. You do not need to remove the holder itself — just the battery. Use a plastic or wooden stick (a toothpick or plastic tweezers work well) to gently pry the battery upward. Metal tools can scratch the movement or cause a short circuit.
If the battery is held down by a metal clip or spring, lift that clip first, then slide the battery out. Some Casio models have a small plastic insulator under the battery; note which side faces up before you remove it, because it must go back the same way.
Note the battery type and buy a replacement
The battery itself is printed with a code — SR626, LR626, SR920, or similar. Write this code down or take a photo. This code tells you the exact size and chemistry you need. Do not guess; a battery that is slightly too thick will not fit, and a battery with the wrong voltage will damage the watch.
You can buy the correct battery at a pharmacy (CVS, Walgreens), a big-box electronics store (Best Buy), a jewelry store, or online. Prices are usually between two and five dollars. Some watch repair shops will replace the battery for you for a fee of ten to twenty dollars if you prefer not to do it yourself.
Install the new battery and test it
Before you close the case, insert the new battery into the holder with the positive side facing up (the side that was facing up on the old battery). Press it down gently until it sits flat. If there was a metal clip holding the old battery, make sure that clip is in place over the new battery.
Press a button on the watch to see if it responds. The display should light up or the second hand should move. If nothing happens, the battery may be inserted upside down — flip it and try again. If it still does not work, the battery may be defective; try a fresh one from a different package.
Close the case back and seal it
Once the watch is working, align the case back with the case body. The back usually has a small notch or mark that lines up with a corresponding mark on the case. Press the back down firmly and evenly, then insert the screws and tighten them in a cross pattern (top, bottom, left, right) to avoid warping the back.
Do not over-tighten the screws. They should be snug enough that the back does not move, but not so tight that you strip the threads or crack the plastic. If your Casio is water-resistant, the case back may have a rubber gasket or seal; make sure it is clean and in place before you close the back, or water may seep in.
What to do if the case back is glued or sealed
Some Casio models, especially digital sports watches and G-Shocks, have case backs that are glued or sealed rather than screwed. These require a different approach. You will need a case opener tool with a flat blade and steady hands. Insert the blade into the seam between the case and the back, and gently work your way around the perimeter, prying a little at a time.
Once the back is off, you can remove and replace the battery the same way. When you close it, you will need to explore a new adhesive seal — a thin bead of clear silicone sealant around the edge of the back. Let it cure for 24 hours before wearing the watch. If you are not comfortable with this process, a watch repair shop can do it for you.
Frequently Asked Questions
What if I lose a screw when I open the case?
Small watch screws are straightforward to lose. If you drop one, search the area where you were working with a flashlight — they are shiny and usually land nearby. If you cannot find it, you can buy replacement screws at a watch supply store or online; bring the watch with you or measure the screw diameter first. Most Casio screws are between 1.5 and 2 mm.
Can I use any battery that fits, or does it have to be the exact model?
It must be the exact model printed on the old battery. The code tells you the size, thickness, and voltage. A battery that is slightly thicker will jam the case back; a battery with the wrong voltage can damage the watch circuit. Always match the code exactly.
How long does a Casio watch battery usually last?
Most Casio batteries last between two and five years, depending on the watch model and how often you use features like the backlight or alarm. Digital watches with constant displays drain batteries faster than analog watches. When the battery dies, the watch will stop or the display will fade.
Is it safe to open a water-resistant Casio watch myself?
Yes, if you are careful. The main risk is damaging the rubber gasket that seals the case back. Before you close it, inspect the gasket for cracks or dirt. If it looks damaged, replace it with a new one from a watch supply store. If the gasket is fine, clean it gently and reinstall it in the same position.
What if the watch still does not work after I put in a new battery?
First, flip the battery over — it may be upside down. If that does not work, try a fresh battery from a different package; the first one may be defective. If a second battery does not work, the watch circuit may be damaged, and a repair shop will need to look at it. Do not keep trying different batteries, as this can drain them quickly.