Your keyless entry fob runs on a coin-cell battery that dies every few years

When your key fob stops locking or unlocking your car from a distance, the battery inside is almost always the culprit. The fob contains a small coin-shaped battery—usually a CR2032, CR2025, or similar size—that powers the transmitter. These batteries last between three and four years on average, depending on how often you use the fob and which model you own.

Replacing it is one of the cheapest and easiest repairs you can do yourself. The battery costs between $3 and $8, the fob itself almost never needs replacement, and the whole job takes about five minutes. You do not need a mechanic, a dealership, or any special tools beyond a coin or a small flathead screwdriver.

Key Takeaways

  • Keyless fob batteries are coin-cell types (CR2032 is most common) that cost $3 to $8 and last three to four years.
  • You can open most fobs by prying gently along the seam with a coin or flathead screwdriver, or by pressing a small release button on the back.
  • Note which side of the battery faces outward before you remove it, because the new battery must go in the same way.
  • If the fob still does not work after battery replacement, the transmitter circuit may be damaged and the fob itself may need replacement.

How to identify which battery your fob uses

The easiest way is to open the fob and look at the battery itself. You will see a number printed on the flat side—CR2032, CR2025, or CR2016 are the most common. Write this number down or take a photo before you go to the store.

If you want to know before opening it, check your owner's manual or search online for your car's year, make, and model plus "key fob battery." Most manufacturers use the same battery across a generation of vehicles, so the answer is usually one search away. You can also call your dealership parts department and give them your vehicle identification number (VIN)—they will tell you the exact battery type in seconds.

Opening the fob without damaging it

Most fobs open in one of two ways. The first is a seam that runs around the edge where the two plastic halves meet. Slide a coin or the flat end of a small screwdriver into this seam and twist gently to pry the halves apart. Start at one corner and work your way around; do not force it at one spot or you will crack the plastic.

The second method is a small button or slot on the back. Press or slide this release, and the battery cover or one half of the fob will pop out. Check your fob's back side before you start prying—if you see a button or slot, try that first.

Once the fob is open, you will see the battery sitting in a small metal holder. Note which side faces up—the positive side (marked with a + symbol) or the negative side. This matters. The new battery must go in the same way, or the fob will not work.

Removing the old battery and installing the new one

Gently pry the old battery out of its holder using your fingernail or the edge of a coin. Do not use excessive force; the holder is plastic and can break. Once the battery is out, inspect the metal contacts inside the holder. If they look corroded or dark, wipe them lightly with a dry cloth or a pencil eraser to remove any buildup.

Slide the new battery into the holder with the same side facing up as the old one. The battery should sit flat and snug. Press down gently to make sure it is seated properly. Close the fob by pressing the two halves together until you hear or feel a click. Test the fob by standing near your car and pressing the lock and unlock buttons.

What to do if the fob still does not work

If you replaced the battery and the fob still does not lock or unlock your car, the transmitter circuit inside the fob is likely damaged. Water damage, a hard drop, or age can break the circuit board even if the battery is good. In this case, the fob itself needs replacement, not just the battery.

You have two options: buy an aftermarket fob online (usually $15 to $40) or order one from your dealership (typically $50 to $150 depending on the vehicle). Aftermarket fobs work with most cars, but some vehicles require programming at a dealership. Check your owner's manual or call your dealership to confirm whether a replacement fob will work with your car or if it needs to be programmed.

Where to buy replacement batteries

Coin-cell batteries are sold at pharmacies, grocery stores, hardware stores, and online retailers. Walgreens, CVS, and similar chains stock them in the watch and battery section. Home Depot and Lowe's carry them near the tools. Amazon and eBay sell them in bulk packs of 5 or 10 for less per battery than buying one at a time.

If you are unsure which battery your fob uses, bring the fob with you to the store and open it there. Staff at most retailers will help you match the battery number. Buying online is cheaper if you are willing to wait a few days for shipping, but a single battery from a local store costs only a few dollars more and you can replace it when ready.

Preventing premature battery drain

Keyless fob batteries drain faster if you use the fob constantly, expose it to extreme heat or cold, or carry it in a pocket where it gets pressed repeatedly. You cannot prevent the battery from dying eventually, but you can slow it down by using the fob only when necessary and storing it in a cool, dry place away from direct sunlight.

If your fob battery dies much sooner than three years—within a year or two—the transmitter may be stuck in a transmitting state, draining power continuously. This usually means the circuit board is failing. In that case, replacing the battery will not solve the problem; you will need a new fob.

Frequently Asked Questions

Can I use a different battery size if I cannot find the exact one?

No. The battery holder is sized for a specific coin-cell type, and using the wrong size will either not fit or will not make proper contact with the metal terminals. Always use the exact battery number printed on the old battery or listed in your manual.

What if I drop the battery or lose it while replacing it?

Coin-cell batteries are small and straightforward to lose. Keep the old battery nearby as a reference for size and polarity, and work over a table or towel so you can see if it falls. If you lose it, the battery number is printed on the old one, so you can order a replacement online or buy one at a store.

Do I need to reprogram the fob after changing the battery?

No. The battery powers the transmitter, but it does not store the programming code. Your car already knows the fob's code, so a new battery will work when ready without any reprogramming.

Is it safe to handle these batteries?

Coin-cell batteries are safe to touch and handle with bare hands. They contain a small amount of lithium or alkaline material, but they are sealed and designed for consumer use. Wash your hands after handling if you prefer, but there is no danger from normal contact.

What should I do with the old battery?

Most communities accept used batteries at recycling centers or hazardous waste collection events. Some retailers like Best Buy and Home Depot also take old batteries for free. Do not throw it in the trash if your area has a battery recycling program, as lithium batteries can pose a fire risk in landfills.