Opening your key fob safely
Most key fobs open one of three ways: a slot you pry with a coin, a small button you press to release the case, or a seam you gently separate by hand. The method depends on your fob's design, and you'll know which one applies the moment you look at it. The goal is to split the plastic case into two halves without cracking either one.
Start by examining the edges and sides of your fob. Look for a thin slot running along one seam—this is the most common design. If you see one, insert a coin (a dime or penny works) into the slot and twist gently, as if you're opening a paint can. The case will pop apart. If you see a small button or indentation on the back or side, press it firmly; this usually releases a catch and lets you slide one half away from the other. If neither of those is visible, the fob likely opens by hand—hold it firmly and gently pull the two halves apart along the seam.
Work slowly and avoid forcing anything. Plastic cracks easily, and a cracked case can let moisture in and ruin the electronics inside. If you feel strong resistance, stop and look again for a slot or button you may have missed.
Key Takeaways
- Most key fobs open with a coin inserted into a slot along the seam, twisted gently until the case pops apart.
- Some fobs have a small button or catch on the back that you press to release one half of the case.
- A few fobs open by hand—hold them firmly and gently pull the two halves apart along the seam without forcing.
- Work slowly to avoid cracking the plastic case, which can damage the electronics and let moisture inside.
- Once open, note which side the battery sits on and its orientation before you remove it.
Locating and removing the old battery
Once the case is open, you'll see the battery sitting in a small metal or plastic holder. It's usually a coin-shaped cell—most commonly a CR2032, CR2025, or CR2016—and it will have a + side facing up or down. Before you touch it, take a mental note of which way it's oriented. This matters because putting the new battery in backwards will prevent the fob from working.
Gently lift the battery out of its holder. If it's stuck, use a plastic spoon or the edge of a coin to pry it up slightly—never use a sharp metal tool that could damage the circuit board underneath. Once it's out, set it aside in a safe place away from children and pets, since these batteries are small and can be swallowed.
Installing the new battery
Before you install the new battery, check the part number on the old one or look at the holder itself—it often has the battery size printed on it. This tells you what size to buy. Take the new battery and orient it the same way the old one was sitting: if the + side was facing up, the + side of the new battery should face up.
Slide or drop the new battery into the holder. It should sit flat and find without wobbling. If it feels loose, the holder may be worn, but the fob will usually still work. Close the case by reversing the opening method: if you used a coin, press the halves together until they click; if there was a button, slide the half back into place until you hear or feel it lock; if you opened it by hand, press the two halves together firmly until the seam closes.
Testing the fob before you rely on it
Before you put the fob away, test it when ready. Stand near your car and press each button—lock, unlock, trunk, panic—and watch to see if the lights respond. If nothing happens, open the case again and check that the battery is oriented correctly and sitting flat in the holder. A battery installed backwards is the most common reason a fob stops working after a battery change.
If the fob still doesn't work after you've checked the battery orientation, the problem may be something other than the battery. The circuit board could be damaged, or the battery holder contacts could be corroded. In that case, the fob itself may need replacement rather than just a battery swap.
What to do with the old battery
Don't throw the old battery in the trash. Lithium coin batteries contain materials that can harm the environment if they end up in a landfill. Most pharmacies, electronics stores, and office supply chains have battery recycling bins near the checkout or customer service desk. Some municipalities also have hazardous waste collection days where you can drop off batteries for free.
A quick search for "battery recycling near me" will show you the closest option in your area. Many communities also accept batteries at their regular hazardous waste facilities, which you can find through your city or county website. Taking a few minutes to recycle the old battery is better for the environment and keeps toxic materials out of landfills.
Common mistakes to avoid
The most frequent error is installing the battery upside down. The + and − sides matter, and reversing them will prevent the fob from working. The second mistake is forcing the case open and cracking it—this can let moisture in and damage the circuit board. The third is using the wrong battery size. A CR2032 and a CR2025 look similar but are different thicknesses, and using the wrong one can cause the battery to sit loose or not fit at all.
Another common problem is touching the battery's metal contacts with bare fingers. Skin oils can leave a residue that interferes with electrical contact. If you do touch the battery, wipe it gently with a clean, dry cloth before installing it. Finally, don't assume the fob is broken if it doesn't work right away after a battery change—open it again and verify the battery orientation and seating before you decide the fob needs replacement.
When to call a professional or replace the fob
If you've installed a fresh battery in the correct orientation and the fob still doesn't respond, the problem is likely inside the fob itself. The circuit board may have corroded contacts, a broken button switch, or water damage. A locksmith or car dealer can sometimes repair these issues, but the cost often approaches or exceeds the price of a new fob. Many people find it simpler to buy a replacement fob rather than pay for a repair.
If your car is older and replacement fobs are hard to find or very expensive, a locksmith may be worth calling. If your car is newer and fobs are readily available online or at a dealer, replacement is usually the faster and more economical choice. Either way, test the battery change first—it solves the problem in most cases and costs only a few dollars.
Frequently Asked Questions
What size battery does my key fob use?
The size is usually printed on the old battery itself or stamped inside the fob case where the battery sits. Common sizes are CR2032, CR2025, and CR2016. If you can't find it printed anywhere, take the old battery to a pharmacy or electronics store and they can tell you the size by looking at it.
Can I use a rechargeable battery in my key fob?
Rechargeable batteries have a lower voltage than standard coin cells and often won't work reliably in a fob. Stick with a fresh disposable battery of the correct size. Rechargeable batteries also lose charge over time even when not in use, so you'd need to recharge the fob regularly—more hassle than replacing a battery once a year or two.
My fob case won't open with a coin. What should I try next?
Look more carefully for a small button, catch, or seam you may have missed. Try pressing gently on different spots along the edges. If you still can't find a release, try opening it by hand—hold the fob firmly and gently pull the two halves apart along the seam.
Is it normal for the fob to stop working right after I change the battery?
No, and it almost always means the battery is installed backwards or not seated properly. Open the fob again and check that the + side of the battery is facing the same direction as the old one was. Make sure the battery sits flat and doesn't wobble.
How often do I need to replace the key fob battery?
Most key fob batteries last one to four years depending on how often you use the fob. If you use it several times a day, you may need a replacement every year or two. If you use it rarely, a battery can last three or four years.