Key fobs run on small coin-cell batteries that last one to four years

Your car key fob contains a small round battery, usually a CR2032, CR2025, or CR2016. These are coin-cell batteries about the size of a dime. The battery powers the radio transmitter that sends the lock and unlock signal to your car. When the battery dies, the fob stops working—but replacing it takes less than a minute and costs two to five dollars.

The exact battery type depends on your car's make and model. Most common fobs use CR2032, which is the thickest and longest-lasting of the three. Some older or compact fobs use CR2025 or CR2016 instead. You can find the correct type printed on the battery itself once you open the fob, or check your owner's manual.

Key Takeaways

  • Most key fobs use a CR2032 coin-cell battery that you can buy at any drugstore, supermarket, or hardware store for two to five dollars.
  • A fob battery typically lasts one to four years depending on how often you use the buttons and the quality of the battery brand.
  • You can replace the battery yourself by prying open the fob case with a coin or flathead screwdriver—no tools or special knowledge required.
  • If your fob still does not work after replacing the battery, the problem is likely a worn button contact or water damage inside the case, not the battery itself.

How to open your fob and see what battery it uses

Most key fobs have a seam running around the edge where the two plastic halves meet. Slide a coin (a penny or dime works well) or a flathead screwdriver into the seam and twist gently. The case will pop open, usually splitting into a front and back half. Do not force it—if it does not budge, try a different spot along the seam.

Once the case is open, you will see the battery sitting in a small metal holder. The battery is stamped with its type number: CR2032, CR2025, or CR2016. Write down this number or take a photo with your phone. Some fobs have a small circuit board attached to one half; handle it carefully but do not worry about damaging it—these boards are tough.

If your fob has a screw holding the case together instead of a snap seam, use a small Phillips or flathead screwdriver to remove it. Keep the screw in a safe place so you do not lose it.

Replacing the battery step by step

Pop the old battery out of its metal holder by pressing gently on one edge. The battery will flip out. Look at the new battery and note which side is marked with a plus sign (+)—that is the positive side. In most fobs, the positive side faces up toward you when you are looking at the open case.

Slide the new battery into the metal holder with the positive side facing the same direction the old one was facing. Press down gently until it clicks or sits flat. Do not force it. Close the fob case by pressing the two halves together until they snap. If your fob had a screw, replace it now.

Test the fob by pressing the lock and unlock buttons while standing near your car. You should hear the car respond or see the lights flash. If nothing happens, open the fob again and check that the battery is sitting flat in its holder and facing the right direction.

Why your fob battery dies faster than expected

A coin-cell battery in a key fob usually lasts one to four years. If yours dies in less than a year, one of a few things is happening. The most common cause is a button that sticks or stays pressed down inside the case, draining the battery constantly. Water inside the case—from rain, a spill, or sweat in your pocket—can also drain the battery much faster than normal.

Using the fob very frequently, like pressing the buttons dozens of times a day, will shorten battery life. Some people also buy very cheap batteries from dollar stores or gas stations; these are often old stock and do not hold a charge as long as batteries from a pharmacy or electronics store.

If you replace the battery and the fob dies again within a few weeks, the problem is not the battery. Open the fob again and look for water droplets, corrosion on the metal contacts, or a button that does not spring back when you press it. Any of these means the fob itself needs repair or replacement, not just a new battery.

Where to buy replacement batteries

Coin-cell batteries are sold almost everywhere. Check the pharmacy section of any supermarket, drugstore, or big-box retailer. They are also at hardware stores, car parts stores, and dollar stores. Online retailers like Amazon sell them in bulk packs of four or more, which is cheaper per battery if you have multiple fobs or devices that use them.

Battery brands matter slightly. Duracell, Energizer, and Panasonic are reliable and last the full rated lifespan. Very cheap generic batteries sometimes die months early. For a fob you use every day, spending an extra dollar on a name brand is worth it.

When you buy, double-check the package to make sure it says CR2032 (or whichever type your fob uses). The numbers look similar—CR2032, CR2025, CR2016—and buying the wrong one means a wasted trip home.

What to do if the fob still does not work after replacing the battery

If you installed a fresh battery and the fob still does not respond, the battery was not the problem. The most likely culprit is worn button contacts. Inside the fob, each button sits on top of a rubber pad with a conductive coating. After thousands of presses, this coating wears away and the button no longer completes the circuit. You can sometimes fix this by cleaning the contacts with a pencil eraser, but it is not a permanent solution.

Water damage is the second most common reason a fob stops working. If you have dropped it in water, spilled liquid on it, or carried it in a sweaty pocket, moisture inside the case can corrode the circuit board or the battery contacts. If you suspect water damage, open the fob and let it sit in a warm, dry place for 24 hours before reassembling it. If that does not work, the fob needs professional repair or replacement.

A third possibility is that the transmitter itself has failed. This is rare and usually happens only after years of heavy use. If the battery is fresh, the contacts look clean, and the buttons work mechanically, the radio transmitter inside the circuit board may have stopped functioning. At that point, you will need a replacement fob from your car dealer or a locksmith.

Frequently Asked Questions

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

No. CR2032, CR2025, and CR2016 are different thicknesses and voltages. Using the wrong type can damage the fob's circuit board or cause the buttons to work unpredictably. Always use the exact type stamped on your old battery or listed in your owner's manual.

How do I know which side of the battery goes up?

The side marked with a plus sign (+) is the positive terminal and should face up toward you when the fob is open. The blank side is negative. If you install it backwards, the fob will not work, but it will not damage anything—just flip it over and try again.

Is it safe to replace the battery myself?

Yes. Coin-cell batteries are safe to handle with your bare hands. They produce no heat and carry very little current. The only real risk is dropping a small battery and losing it, so work over a table or sink where you can see it.

Why does my fob work sometimes but not always?

This usually means the battery is dying but not completely dead yet. Replace it with a fresh one. If the problem continues after replacement, the button contacts are likely worn and need cleaning or the fob needs repair.

Can I recharge a coin-cell battery?

No. CR2032, CR2025, and CR2016 batteries are not rechargeable. Once they die, throw them away and install a new one. Some retailers have battery recycling programs if you want to dispose of the old one responsibly.