Most key fob batteries take five minutes to swap out yourself

You can replace a key fob battery without a trip to the dealership or a locksmith. The battery sits in a compartment inside the fob, held by a small clip or spring. You pry the fob open with a coin or flathead screwdriver, slide out the old battery, and slide in a new one—the whole job takes longer to find the right battery size than to do the work.

The battery type varies by car brand and fob model. Common sizes are CR2032, CR2025, and CR2016. Your owner's manual lists the correct size, or you can check the old battery itself once you open the fob. A replacement battery costs two to five dollars at any pharmacy, grocery store, or hardware store.

Key Takeaways

  • Open the fob by inserting a coin or flathead screwdriver into the seam and twisting gently until the two halves separate.
  • Note the battery size printed on the old battery before you remove it, so you buy the exact replacement.
  • Slide the old battery out from under the metal clip or spring, then slide the new battery in with the positive side facing up.
  • Press the fob halves back together until they click, and test the buttons to confirm the new battery works.
  • If the fob still does not work after a new battery, the problem is likely a worn button contact or water damage inside the fob.

Finding the seam and opening the fob

Look at the edge of your key fob for a thin line running around the perimeter. This is the seam where the two plastic halves meet. Insert a coin (a penny or dime works well) or a flathead screwdriver into the seam, positioning it so the edge of the coin or screwdriver blade sits in the groove.

Twist the coin or screwdriver gently—do not force it. You are trying to separate the two halves, not pry them apart with brute force. A quarter-turn is usually enough to create a gap. Once you see a gap, you can often use your fingernail or the coin to pry the halves apart the rest of the way. If the fob is very tight, work your way around the seam, twisting at two or three points, rather than trying to force one spot open.

Some fobs have a small notch or arrow marking the correct spot to insert the coin. If you see one, start there. If the fob still will not budge after gentle twisting, check your owner's manual—a few models have a button or latch you must press first.

Identifying and removing the old battery

Once the fob is open, you will see a small round or rectangular battery held in place by a metal clip or spring. The battery has a number printed on it: CR2032, CR2025, or CR2016 are the most common. Write down this number or take a photo of it before you remove the battery. You need this exact size when you buy the replacement.

Gently lift the metal clip or spring away from the battery. The battery should slide out easily. If it does not, do not pry at it—lift the clip a bit higher and try again. Once the battery is out, look at which side was facing up. The positive side (marked with a + sign) should face upward when you insert the new battery.

Inspect the inside of the fob while it is open. If you see corrosion (white or green crusty deposits) or water damage, the fob may not work even with a new battery. Corrosion usually means the old battery leaked, and water damage suggests the fob has been exposed to moisture. In either case, a new battery is worth trying, but be prepared that the fob may need professional repair.

Installing the new battery

Buy a replacement battery that matches the number on the old one. You can find these at pharmacies, grocery stores, hardware stores, and online retailers. The cost is usually two to five dollars. Do not buy a generic "key fob battery"—the size matters, and the wrong size will not fit or will not work.

Slide the new battery into the compartment with the positive side (+ mark) facing upward. The metal clip or spring should hold it in place. If the battery feels loose, lift the clip slightly and reseat the battery. It should sit flat and not wiggle.

Before you close the fob, press one of the buttons to see if the light comes on (if your fob has a light). This tells you the battery is making contact and the fob is getting power. If nothing happens, remove the battery and flip it over—you may have inserted it upside down. Once the light comes on or you hear a click, you are ready to close the fob.

Closing the fob and testing it

Align the two halves of the fob so the seam lines up evenly. Press them together firmly until you hear or feel a click. The fob should be snug and not have any gaps. If one side is higher than the other, pop it back open and reseat the battery—a loose battery can prevent the halves from closing properly.

Test the buttons on your car. Press the lock button and listen for the car to lock. Press the unlock button and listen for the car to unlock. If the fob works, you are done. If it does not work, try the battery flip test again: open the fob, remove the battery, flip it, and reinstall it. Sometimes a battery that looked right was actually upside down.

If the fob still does not work after trying a new battery and flipping it, the problem is likely inside the fob itself. Worn button contacts or water damage can prevent the fob from sending a signal even with fresh power. At that point, a locksmith or dealership can repair or replace the fob.

Common mistakes that prevent the battery from working

The most common mistake is installing the battery upside down. The positive side (marked with +) must face upward toward the buttons. If you installed the battery and the fob does not work, open it again and flip the battery. This fixes the problem about half the time.

Another common mistake is buying the wrong battery size. CR2032, CR2025, and CR2016 look similar but are not interchangeable. A battery that is too small will rattle inside the compartment and may not make good contact. A battery that is too large will not fit. Always check the number on the old battery before you buy a replacement.

A third mistake is not seating the battery fully under the metal clip. If the clip is not holding the battery down, it may not make contact with the terminals. Open the fob and make sure the battery sits flat and the clip is pressing down on it.

Finally, do not assume a new battery will fix a fob that has been wet or corroded. If you see white or green deposits inside the fob, or if the battery compartment smells like chemicals, the fob may have internal damage that a new battery cannot repair.

What to do if the new battery does not work

If you have installed a new battery of the correct size with the positive side facing up, and the fob still does not work, try these steps. First, open the fob again and clean the battery terminals (the metal contacts inside the compartment) with a dry cloth or a pencil eraser. Dirt or corrosion on the terminals can prevent the battery from making contact.

Second, check the button contacts. Press each button and look for a small metal dome or contact under the button. If the contact looks worn, discolored, or flat, the button may not be sending a signal even though the battery is good. This is a sign the fob needs professional repair.

Third, test the fob at different distances from your car. A fob with a weak battery may work from a few feet away but not from across a parking lot. If the fob works at close range, the battery is probably fine and the fob's range is just reduced.

If none of these steps work, the fob likely has internal damage that a new battery cannot fix. A locksmith or your car's dealership can repair or replace the fob. Repair usually costs thirty to eighty dollars, depending on the car brand and whether the locksmith can fix the existing fob or needs to program a new one.

Frequently Asked Questions

Can I use any round battery, or does it have to be the exact size?

It has to be the exact size. CR2032, CR2025, and CR2016 are not interchangeable. A battery that is too small will not make contact. A battery that is too large will not fit. Check the number on your old battery and buy that exact size.

What if I cannot get the fob open?

Try inserting the coin or screwdriver at a different spot along the seam. Some fobs have a notch or arrow showing the correct insertion point. If the fob is still stuck, check your owner's manual—a few models have a hidden button or latch. If you are still unable to open it, a locksmith can open it for you, though this costs more than doing it yourself.

How long does a key fob battery last?

Most key fob batteries last three to four years with normal use. If you use the fob frequently, the battery may wear out sooner. If you rarely use the fob, it may last longer. A battery that is losing power will show signs: the fob will only work from a few feet away, or you will have to press the button multiple times.

Is it safe to replace the battery myself, or should I go to a dealership?

It is safe to replace the battery yourself. The fob contains no dangerous parts, and the battery is a standard consumer battery sold in stores everywhere. A dealership will do the same job for twenty to fifty dollars, so replacing it yourself saves money and time.

What should I do with the old battery?

Most retailers that sell batteries also accept old batteries for recycling. Take the old battery back to a pharmacy, grocery store, or hardware store and ask where to drop it off. Do not throw it in the trash—batteries contain materials that should be recycled.