Open the key fob the right way to avoid breaking the case
Most key fobs split into two halves along a seam that runs around the edge. Look for a small slot or notch on one side — 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; the case will pop apart without force.
Some fobs have a screw instead of a snap closure. If you see a small screw on the back or side, use a screwdriver that fits the head exactly — too loose and you strip it, too tight and you crack the plastic. Set the screw somewhere you won't lose it, like a small dish or envelope.
Once the case is open, you will see the battery sitting in a metal holder. Note which side faces up — the flat side or the side with a bump. This matters when you put the new battery in.
Key Takeaways
- Most key fobs open by prying along the seam with a flat tool; some have a screw you must remove first.
- The battery sits in a metal holder and has a correct direction — the flat side or the bumped side faces up depending on your fob model.
- Buy a replacement battery by the three-digit code printed on the old one, usually CR2032, CR2025, or CR2016.
- Slide the old battery out, slide the new one in the same direction, and snap or screw the case shut.
Find the right replacement battery by the code on the old one
The battery in your key fob has a three-digit code stamped or printed on it. The most common code is CR2032, but you may also see CR2025, CR2016, or CR2430. This code tells you the exact size and chemistry you need. Do not guess — buying the wrong size means the battery won't fit or won't power the fob.
Take the old battery to a pharmacy, grocery store, or hardware store and match it to the replacement. Coin-cell batteries cost between one and three dollars. You can also order them online, but buying in person means you can test the fob right away instead of waiting for shipping.
Remove the old battery and insert the new one in the same direction
Once the case is open and you can see the battery, note which side faces up. If the flat side faces up, the new battery's flat side must also face up. If the bumped side (the positive terminal) faces up, the new battery's bumped side goes up. Putting it in backwards means the fob will not work.
Slide the old battery out of the metal holder with your fingernail or a plastic tool. Do not use a sharp metal tool — you can scratch the circuit board inside. Slide the new battery in the same way, making sure it sits flat in the holder and the correct side faces up.
Close the case and test the fob before you leave the store
Snap the two halves of the case back together by pressing firmly along the seam until you hear or feel a click. If your fob has a screw, insert it and tighten it by hand first, then use the screwdriver to snug it down — do not over-tighten or you will crack the plastic.
Test the fob right away by pressing each button while standing near your car. You should hear the locks click or see the lights flash. If nothing happens, open the case again and check that the battery is facing the right direction and sitting fully in the holder. If the fob still does not work after you flip the battery, the circuit board may be damaged and the fob may need to be replaced.
Common mistakes that prevent the fob from working after battery replacement
The most common error is installing the battery backwards. The flat side and the bumped side look similar, so it is straightforward to mix them up. If your fob does not work after you close it, open it again and flip the battery 180 degrees. This fixes the problem nine times out of ten.
The second mistake is not seating the battery fully in the metal holder. If the battery is tilted or sitting at an angle, it will not make good contact with the terminals. Push it down gently until it lies flat and does not move when you tap the case.
The third mistake is over-tightening the screw on fobs that have one. This cracks the plastic case and can damage the circuit board inside. Tighten the screw until it is snug, then stop — you should not need to use force.
When to replace the whole fob instead of just the battery
If you have replaced the battery, checked that it is facing the right direction, and the fob still does not work, the problem is likely inside the fob itself. Water damage, a cracked circuit board, or worn-out buttons can all prevent the fob from working even with a fresh battery.
A replacement fob costs between thirty and one hundred dollars depending on your car's make and model. You can buy one from a car dealer, an auto parts store, or online. Some fobs can be programmed by the owner; others must be programmed by a dealer. Check your car's manual or call the dealer to find out which type you have.
Frequently Asked Questions
Can I use a different battery size if I can't find the exact code?
No. A battery that is too large will not fit in the holder, and a battery that is too small will not make contact with the terminals. The three-digit code is specific to the size and voltage your fob needs. If you cannot find the exact code at a local store, order it online or ask the store to order it for you.
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 many times per day, the battery may wear out faster. If you use it rarely, it may last longer. There is no way to predict exactly when it will die, so replace it as soon as the fob stops working reliably.
What should I do with the old battery?
Coin-cell batteries contain small amounts of lithium or other chemicals and should not go in the trash. Most pharmacies and electronics stores have a battery recycling bin near the checkout. Drop the old battery there, or ask a store employee where to put it.
Will replacing the battery erase my fob's programming?
No. The programming is stored in the circuit board inside the fob, not in the battery. Replacing the battery will not erase it, and your fob will work the same way it did before the battery died.
Why does my fob work sometimes but not other times after I replaced the battery?
This usually means the battery is not making full contact with the terminals. Open the fob and check that the battery is sitting flat in the holder and not tilted. If it is tilted, push it down gently until it lies flat. If the problem continues, the metal contacts inside the holder may be bent or corroded, and the fob may need to be replaced.