Most key fob batteries come out by sliding or prying open the case
A dead key fob battery is one of the easiest car problems to fix yourself. The battery sits inside a plastic case that opens without tools—usually by sliding a small button or wedge, or by prying gently with a coin or flathead screwdriver. Once the case is open, you remove the old battery, note which side faced up, and drop in a new one of the same size. The whole job takes about five minutes and costs between $3 and $8 for the battery.
The hardest part is knowing which battery size your fob uses. Your car's manual lists it, or you can open the fob and read the number printed on the old battery itself. Common sizes are CR2032, CR2025, and CR2016—the numbers tell you the diameter and thickness. Any pharmacy, grocery store, or hardware store sells these batteries in the watch or electronics aisle.
Key Takeaways
- Most key fobs open by sliding a button on the edge or prying gently with a coin—check your manual or the fob itself for the exact method.
- Write down the battery size (usually printed on the old battery) before you go shopping, or take the old battery with you to match it.
- When you install the new battery, the side marked with a + or flat side should face up—check the old battery's position if you are unsure.
- If the fob still does not work after you replace the battery, the problem is likely a broken button contact or water damage, not the battery itself.
Find out how your fob case opens
The case design varies by car brand and year. Most fobs have a small slot or button on one edge—slide it in the direction of the arrow (if there is one) to separate the two halves. Some fobs have a seam that runs around the edge; use a coin or the edge of a flathead screwdriver to gently pry the halves apart, starting at the seam. Work slowly and wiggle the tool as you go so you do not crack the plastic.
A few older or luxury fobs use a screw or a hidden latch. Check your owner's manual first—it shows the exact opening method with a diagram. If you cannot find the manual, search online for "[your car year and model] key fob battery replacement" and look for a photo guide. Forcing the wrong way can break the case or the internal contacts.
Identify and remove the old battery
Once the case is open, you will see a small coin-shaped battery sitting in a plastic holder. The battery has a number stamped on top—write this down or take a photo. This number is your shopping list. The battery also has a + symbol or flat side on top and a − symbol or domed side on the bottom; note which way it sits before you remove it.
Gently pry the battery out of the holder with your fingernail or a plastic tool. Do not use a metal screwdriver directly on the battery, as it can cause a short. Once it is out, set it aside. If the battery is stuck, a tiny dab of water on the edge can help it slide out, but do not soak the fob.
Install the new battery the same way the old one faced
Drop the new battery into the holder with the + side facing up, matching the position of the old battery. Press down gently until it clicks or sits flat. Do not force it—the battery should rest in the holder without pressure. If it does not sit flat, you may have the wrong size or the wrong side facing up.
Before you close the case, press each button on the fob a few times to make sure it works. You should hear a click or feel resistance when you press. If a button feels mushy or does not click, the internal contact may be dirty or damaged—close the case anyway and test the fob on your car. If it works, you are done. If it does not, the problem is not the battery.
Close the case and test the fob
Slide the two halves back together until they click or sit flush. If your fob pries open, press the edges together firmly until the seam closes completely. Do not force it—if the halves do not want to close, you may have the battery in backwards or the case may be slightly misaligned. Open it again and check.
Walk to your car and test each button—lock, unlock, trunk, panic, or whatever your fob has. Stand a few feet away so you can see the lights respond. If the fob works, you are finished. If it does not, try replacing the battery again, making sure the + side faces up. If it still does not work after a second try, the problem is likely inside the fob, not the battery.
Where to buy the right battery
Pharmacies like CVS and Walgreens stock coin-cell batteries in the watch or first-aid aisle. Grocery stores often carry them near the pharmacy or in the electronics section. Hardware stores like Home Depot and Lowe's have them in the electrical aisle. Walmart and Target sell them in the electronics or pharmacy section. Online, Amazon and eBay sell them in bulk packs, which is cheaper if you have multiple fobs or devices.
Bring the old battery or the number written down so you buy the exact size. A CR2032 is not the same as a CR2025, and using the wrong size can damage the fob or not work at all. If you are not sure, ask the store employee—they can match the battery to your fob if you bring it with you.
Common mistakes to avoid
The most common mistake is installing the battery upside down. The + side must face up. If your fob does not work after replacement, open it again and flip the battery. Another mistake is buying the wrong size—always check the number on the old battery before you shop. A CR2032 looks almost identical to a CR2025, but they are different thicknesses and will not work in the wrong fob.
Do not force the case open or closed. If it does not move easily, you are probably using the wrong opening method. Stop and check the manual or a photo guide. Forcing the case can crack the plastic or break the internal contacts, which costs more to fix than the battery itself. If the fob gets wet, let it dry completely before you open it—moisture inside can corrode the contacts and make the battery replacement pointless.
Frequently Asked Questions
How long does a key fob battery last?
Most key fob batteries last three to four years with normal use. Heavy use—pressing the buttons many times a day—can shorten the life to two years. You will notice the range getting shorter before the battery dies completely; if you have to stand closer to your car for the fob to work, the battery is getting weak.
Can I use a rechargeable battery in my key fob?
No. Rechargeable batteries (NiMH) have a different voltage than alkaline coin cells and will not work in a key fob. Stick to single-use alkaline batteries like Energizer or Duracell in the size your fob needs. Some rechargeable coin cells exist, but they are rare and not worth the trouble.
What if the fob still does not work after I replace the battery?
Try the battery again, making sure the + side faces up. If it still does not work, the problem is likely a broken button contact, water damage, or a dead receiver in your car. Test the fob's buttons by pressing them near a smartphone camera—if you see a faint light flash, the fob is sending a signal and the problem is your car's receiver. If you see no light, the fob itself is broken.
Do I need to reprogram my key fob after changing the battery?
No. Changing the battery does not erase the fob's programming. It will work exactly as it did before, as long as the battery is good and installed correctly. Reprogramming is only needed if you buy a new fob or if your car's receiver stops responding to all fobs.
Can I replace the battery in a smart key or push-button fob?
Yes, the process is the same. Smart keys and push-button fobs use the same coin-cell batteries as regular fobs. Open the case the same way, replace the battery, and close it. The fob will work without reprogramming. If your smart key has a physical key blade inside, it may take a bit more care to open without damaging the blade, but the battery replacement itself is identical.