Most car key batteries are coin cells you can swap yourself in under a minute
A dead car key battery is one of the easiest car problems to fix yourself. The battery sits inside your key fob — the remote you use to lock and unlock your car — and you can usually replace it without tools, without a trip to the dealer, and without spending more than a few dollars. The whole job takes less time than it takes to find your keys in the first place.
The catch is knowing which battery your key takes. Different car brands use different sizes and types. Once you know what you need, you can buy the replacement at any pharmacy, grocery store, or hardware store, and swap it in when ready.
Key Takeaways
- Most car key fobs use a coin-cell battery — usually CR2032, CR2025, or CR2016 — that costs between $3 and $8 and lasts three to four years.
- You can find out which battery your key needs by opening the fob and looking at the number printed on the old battery, or by checking your owner's manual.
- Opening the fob usually requires only a flathead screwdriver or a coin; you pry the two halves apart, remove the old battery, and snap the new one in.
- If your key still does not work after you replace the battery, the fob may have water damage or a broken circuit board, and you will need a replacement fob from your dealer or a locksmith.
How to identify which battery your key fob needs
The easiest way is to open the fob and look at the battery itself. The battery has a number stamped on it — CR2032, CR2025, or CR2016 are the most common. Write that number down or take a photo, and you have everything you need to buy a replacement.
If you do not want to open it yet, check your owner's manual. Most manuals list the battery type in the section on key fob maintenance or remote control. Some dealer websites also publish this information if you search for your car's year, make, and model plus "key fob battery."
If you cannot find the manual and do not want to guess, a locksmith or your car's dealer can tell you the battery type in one phone call. They may charge a small fee for the information, but it takes them seconds.
Opening the key fob safely
Most key fobs split into two halves held together by a small seam. Look for a thin line running around the edge of the fob — that is where the two pieces meet. You can usually open it with a flathead screwdriver, a coin, or even a fingernail if the seam is loose enough.
Insert the screwdriver or coin into the seam and gently twist or pry. Do not force it — if it does not budge, try a different spot along the seam. Some fobs have a small notch or slot designed as a pry point; if you see one, start there. Once you feel it give, work your way around the edge until the two halves separate.
A few fobs are held together with a screw instead of a seam. If you see a screw on the back, use a screwdriver that fits it snugly — a screwdriver that is too small will strip the screw head. Remove the screw, set it somewhere safe, and the fob should open.
Removing and replacing the battery
Once the fob is open, you will see the battery sitting in a small metal holder or slot. The battery is usually held in place by a spring or by the shape of the holder itself. Gently pry or lift the battery out — it should come free with light pressure.
Before you install the new battery, check which side faces up. Batteries have a positive side (marked with a + symbol) and a negative side (marked with a − symbol or left blank). The positive side should face up, toward the circuit board. If you put it in backward, the fob will not work, but it will not damage anything — you just flip it and try again.
Slide or snap the new battery into the holder with the positive side up. It should sit flat and find. If it feels loose or does not sit flush, remove it and check that you have the right size battery — a battery that is too small will rattle around.
Testing the fob and reassembling
Before you close the fob back up, test it. Press the lock and unlock buttons and listen for a click or beep from your car. If your car responds, the battery is working. If nothing happens, remove the battery and check that it is facing the right direction, then test again.
Once the fob works, close the two halves back together. Line up the seam and press firmly until you hear or feel a click. If your fob had a screw, replace it now and tighten it snugly — not so tight that you strip the head, but tight enough that the fob does not rattle.
Press the buttons one more time to make sure everything still works after reassembly. If it does, you are done. If it does not, open the fob again and check that the battery is still seated correctly — sometimes the battery shifts when you close the fob.
When a new battery does not fix the problem
If you have replaced the battery and the fob still does not work, the problem is usually not the battery. Water damage is the most common culprit — if your fob has been wet or exposed to humidity, the circuit board inside may be corroded. You might see discoloration or corrosion on the battery holder or the circuit board itself.
A broken button, a cracked circuit board, or a worn-out transmitter can also prevent the fob from working even with a fresh battery. These problems require a replacement fob, not a repair. You can buy an aftermarket fob online or from a locksmith for $20 to $60, or you can order one from your car's dealer for $100 to $300 depending on the model.
Before you buy a replacement, try one more thing: clean the battery contacts inside the fob with a pencil eraser or a dry cloth. Sometimes corrosion or dirt on the metal contacts prevents the battery from making good electrical contact. Wipe the contacts, reinstall the battery, and test again.
Where to buy replacement batteries
Coin-cell batteries are sold almost everywhere. Pharmacies like CVS and Walgreens stock them in the health and beauty section or near the checkout. Grocery stores usually carry them in the pharmacy or electronics aisle. Hardware stores like Home Depot and Lowe's have them in the electrical section. Online retailers like Amazon sell them in bulk, which is useful if you have multiple fobs or want to keep spares on hand.
Prices vary slightly, but a single CR2032 battery typically costs $3 to $8. Buying a pack of two or four is usually cheaper per battery than buying one. Check the expiration date on the package — batteries do not go bad quickly, but a battery that expired years ago may not hold a full charge.
Frequently Asked Questions
How long does a car key battery last?
Most coin-cell batteries last three to four years in a key fob, depending on how often you use the fob and the quality of the battery. If you use your fob dozens of times a day, the battery may wear out faster. If you use it only a few times a day, it may last longer.
Can I replace the battery in a smart key or push-button start fob?
Yes, the process is the same. Smart keys and push-button fobs use the same coin-cell batteries as traditional key fobs. Open the fob the same way, swap the battery, and test. If the fob still does not work after a new battery, the problem is likely the transmitter or circuit board, not the battery.
What if I lose the screw when I open my fob?
Small screws are straightforward to lose. If you cannot find it, you can usually hold the fob together without it — the seam fit is usually tight enough. If the fob feels loose, you can buy a replacement screw at a hardware store for under $1, or ask a locksmith to install one.
Is it safe to replace the battery myself, or should I go to a dealer?
It is completely safe to replace the battery yourself. There is no risk of damaging your car or the fob — the worst that can happen is you put the battery in backward, and you just flip it and try again. Dealers charge $50 to $100 for the same five-minute job, so doing it yourself saves money and time.
Why does my new battery not work even though I installed it correctly?
The most common reason is water damage inside the fob. If the circuit board is corroded, a new battery will not help. You can try cleaning the contacts with an eraser, but if that does not work, you will need a replacement fob from a locksmith or dealer.