Most key fob batteries are coin cells you can swap yourself without tools
A dead key fob battery is one of the easiest car maintenance tasks to fix at home. The battery inside is almost always a coin-cell type—the same flat, round battery you find in watches or calculators—and it costs between $3 and $10. You can replace it in under five minutes with nothing but your fingernail or a flathead screwdriver, and you do not need to visit a dealer or locksmith.
The only real variable is how the fob opens. Some split down the middle like a clamshell. Others have a slot where you slide the battery out. A few have a small screw you remove first. Once you know which type you have, the rest is straightforward.
Key Takeaways
- Key fob batteries are coin cells (usually CR2032, CR2025, or CR2016) that cost $3 to $10 and last three to four years.
- Most fobs open by prying the seam with a flathead screwdriver or fingernail; some slide open or have a small screw on the back.
- Write down the battery type printed on the old battery before you buy a replacement, because different fobs use different sizes.
- If the fob still does not work after you install a new battery, the problem is likely a corroded contact or a broken circuit board, not the battery itself.
Identify your fob type and battery size
Before you open anything, look at the back of your fob. If you see a small screw, you will need a screwdriver that fits it—usually a Phillips head, sometimes a flathead. If you see a seam running around the edge, you will pry it open. If you see a slot or a small tab, you will slide the battery out sideways. Take a photo of your fob with your phone so you remember which type it is.
The battery type is printed on the old battery itself once you get the fob open. Common types are CR2032 (the most common), CR2025, and CR2016. The numbers refer to the size: a CR2032 is 20 millimeters across and 3.2 millimeters thick. Write this number down before you close the fob, because buying the wrong size means the battery will not sit flush and the fob may not work.
Open the fob without breaking the plastic
If your fob has a screw, remove it with the correct screwdriver and set it somewhere you will not lose it—a small dish or a piece of tape works well. The two halves should separate easily once the screw is out.
If your fob has a seam, insert a flathead screwdriver or the edge of a coin into the groove and twist gently. Do not force it; if it does not budge, try a different spot along the seam. The plastic is thin and cracks easily. Once you feel it start to give, work your way around the seam a little at a time rather than prying hard in one spot. The two halves will eventually pop apart.
If your fob has a slot, look for a small tab or arrow pointing to it. Slide a flathead screwdriver into the slot and push gently. The battery holder should slide out of the fob body. This type is the easiest because there is almost no risk of breaking anything.
Remove the old battery and install the new one
Once the fob is open, you will see the battery sitting in a metal holder. It is usually held in by nothing—just gravity and a slight lip. Pry it out with your fingernail or the screwdriver. If it is stuck, a tiny dab of rubbing alcohol around the edge can help loosen corrosion, but usually it comes out easily.
Before you install the new battery, look at the metal contacts inside the fob. They should be shiny and clean. If they are dark, green, or crusty, wipe them gently with a dry cloth or a cotton swab. Corrosion on the contacts is a common reason a fob stops working even after you install a fresh battery.
Slide the new battery into the holder with the positive side (marked with a + or the shiny side) facing up. It should sit flat and flush. If it rocks or sits at an angle, you may have the wrong size battery. Check the number on the old battery again and make sure the new one matches.
Close the fob and test it
If your fob has a screw, line up the two halves and insert the screw. Tighten it by hand first, then with the screwdriver. Do not overtighten; you only need it snug enough that the halves do not separate.
If your fob has a seam, press the two halves together firmly. Start at one corner and work your way around, pressing down until you hear or feel a click. The seam should be flush all the way around. If there is a gap anywhere, the battery may not make contact and the fob will not work.
If your fob has a slot, slide the battery holder back into the fob body until it clicks. Test the buttons right away. If the fob works, you are done. If it does not, remove the battery and check that the contacts are clean and the battery is sitting flat.
What to do if the new battery does not fix it
If you installed a fresh battery and the fob still does not work, the problem is not the battery. The most common culprit is corrosion on the metal contacts inside the fob. Remove the battery again and clean the contacts more thoroughly with a cotton swab dampened with rubbing alcohol. Let them dry completely before you reinstall the battery.
If cleaning the contacts does not help, the circuit board inside the fob may be damaged or the buttons may be worn out. At that point, a replacement fob from a dealer, locksmith, or online retailer is usually cheaper than repair. A new fob typically costs $50 to $200 depending on your car, and some dealers will program it for you while you wait.
If only one button stopped working while the others still work, the problem is usually the rubber pad under that button wearing out. This is also not something you can fix at home; you would need a new fob or a professional repair.
Where to buy a replacement battery
Coin-cell batteries are sold at any pharmacy, grocery store, hardware store, or big-box retailer. They are usually in the watch or battery aisle. A single CR2032 costs $3 to $5 at most places. Online retailers like Amazon sell them in bulk packs of 10 or more for $0.50 to $1 per battery if you want to stock up.
Do not buy the cheapest battery you can find. Cheap coin cells sometimes have poor contact or die faster than name brands. Energizer, Duracell, Panasonic, and Maxell are reliable choices. A quality battery should last three to four years in a key fob before it needs replacing again.
Frequently Asked Questions
Can I use a different battery size if I cannot find the exact one?
No. A CR2032 and a CR2025 look almost identical but are different thicknesses. Using the wrong size means the battery will not sit flush in the holder, the contacts will not make good connection, and the fob will not work. Always match the number on the old battery exactly.
How long does a key fob battery last?
A quality coin-cell battery in a key fob usually lasts three to four years. If you use the fob heavily—pressing the buttons many times a day—it may die sooner. A battery that dies in less than a year usually means the fob has a problem, not that the battery is defective.
What if I lost the screw when I opened the fob?
Take the fob to a hardware store and show them the hole. They can usually match it to a replacement screw for $0.50 to $2. Bring the fob with you so they can test the fit. If you cannot find a match, a small dab of super glue on the seam will hold the two halves together, though you will have to pry it open again if the battery dies.
Is it safe to replace the battery myself, or should I go to a dealer?
It is completely safe to replace it yourself. There is no risk of electric shock or damage to your car. The only risk is breaking the plastic fob if you pry too hard, but that is rare if you work slowly. A dealer will charge $50 to $100 to do the same five-minute job.
Why does my fob work sometimes but not always?
An intermittent fob usually means the battery is dying but not completely dead yet. Replace it with a fresh battery. If the problem continues, the contacts inside are probably corroded or the circuit board is failing. Clean the contacts first; if that does not help, the fob needs replacement.