Open the key fob case first
Most key fobs split into two halves along a seam that runs around the edge. Look for a thin slot or groove on the side of the fob — this is where you insert a flat tool to pry the case open. A flathead screwdriver, butter knife, or coin works well. Insert the tool gently into the slot and twist slightly to separate the two halves. Do not force it; if it does not budge, you may be pushing on the wrong edge.
Some fobs have a small screw instead of a snap-together case. If you see a screw on the back or side, use a screwdriver that fits snugly into the head — a screwdriver that is too small will strip the screw and make it impossible to open. Set the screw somewhere you will not lose it, like a small dish or envelope.
Once the case is open, you will see the battery sitting in a plastic holder. The battery is usually a coin-shaped cell, most commonly a CR2032, CR2025, or CR2016. The numbers refer to the size and thickness. Write down or photograph the battery type before you remove it, so you know what to buy as a replacement.
Key Takeaways
- Insert a flathead screwdriver or coin into the seam around the edge of the fob and gently twist to separate the two halves.
- If your fob has a screw, use a screwdriver that fits the head snugly to avoid stripping it, and keep the screw in a safe place.
- Note the battery type (usually printed on the battery itself) before you remove it so you know what replacement to buy.
- Lift the battery straight out of its holder and replace it with the new one, making sure the positive side faces up.
- Snap or screw the case back together and test the fob before you put the old battery in the trash.
Lift the battery out of its holder
The battery sits in a small plastic cradle or clip. You do not need to pull hard — the battery is held loosely so it can be replaced easily. Use your fingernail or a plastic tool to gently lift one edge of the battery and slide it out. If the battery is stuck, a small plastic spoon or the edge of a credit card can help you pry it up without scratching the fob.
Pay attention to which side of the battery faces up. Batteries have a positive side (marked with a + sign) and a negative side (marked with a − sign or left blank). The positive side almost always faces up toward the circuit board. When you insert the new battery, it must go in the same way.
Insert the new battery correctly
Before you install the new battery, check that the positive side is facing up. Slide the new battery into the holder the same way the old one came out. It should sit flat and click or snap into place. If it does not sit flush, you may have it upside down — flip it and try again.
Do not force the battery into the holder. If it does not slide in smoothly, stop and check the orientation. Forcing a battery in the wrong way can damage the holder or the circuit board and make the fob unusable.
Close the fob case and test it
Line up the two halves of the fob so the seams match. Press them together firmly until you hear or feel a click. If your fob has a screw, insert it back into the hole and tighten it with a screwdriver — snug but not so tight that you strip the screw.
Test the fob by pressing each button while standing near your car. You should hear the car lock or unlock, or see the lights flash. If nothing happens, open the fob again and check that the battery is seated properly and facing the right direction. If the fob still does not work after you reseat the battery, the battery may be defective or the fob may need repair.
Common mistakes to avoid
The most common error is installing the battery upside down. If the fob does not work after you close it, open it again and flip the battery. The positive side must face the circuit board.
Another mistake is buying the wrong battery size. CR2032, CR2025, and CR2016 look similar but are different thicknesses. A battery that is too thick may not fit in the holder, and one that is too thin may not make good contact. Always check the old battery or your fob's manual to confirm the size before you buy a replacement.
Do not leave the fob open for a long time or expose the circuit board to water or dirt. Close it as soon as you have installed the new battery. If you spill liquid on the circuit board while the fob is open, let it dry completely before closing the case.
Where to buy replacement batteries
Coin-cell batteries are sold at most drugstores, supermarkets, hardware stores, and online retailers. A single battery usually costs between one and three dollars. You can also buy them in multipacks if you have several devices that use the same size. Check the price per battery in a multipack — sometimes a single battery is cheaper.
If you are not sure which size to buy, bring the old battery or your fob to the store and ask a staff member to match it. Many stores will also install the battery for you at no extra cost if you buy it there.
Frequently Asked Questions
What if my key fob has no seam and I cannot open it?
Some fobs are sealed and not meant to be opened by the user. If you cannot find a seam or slot after looking carefully at all edges, the fob may need to go to a car dealer or locksmith for battery replacement. Call your car manufacturer or a local locksmith to ask about their battery replacement service.
Can I use a rechargeable battery in my key fob?
Most key fobs are designed for single-use alkaline or lithium coin cells, not rechargeable batteries. Rechargeable batteries have different voltage and may not work reliably in a fob. Stick with the same type of battery that came out of your fob.
How long does a key fob battery last?
A typical key fob battery lasts three to four years with normal use. If you use your fob many times a day, the battery may wear out sooner. If you notice the fob only works when you hold it very close to the car, the battery is running low and should be replaced soon.
What should I do with the old battery?
Coin-cell batteries contain small amounts of toxic materials and should not go in the trash. Most drugstores and electronics retailers have battery recycling bins near the checkout. You can also take old batteries to a local hazardous waste collection site. Call your city or county to find a drop-off location near you.
Will replacing the battery erase my fob's programming?
No. The battery powers the fob but does not store the programming code. Replacing the battery will not erase or change any settings. Your fob will work exactly as it did before once the new battery is installed.