Most car key batteries last three to four years and cost $3 to $10 to replace
A dead car key battery is one of the easiest car problems to fix yourself. The battery inside your key fob powers the buttons that lock and unlock your doors remotely. When it stops working, you do not need a mechanic — you need a new battery, a flathead screwdriver, and five minutes.
The exact steps depend on how your key fob opens, but the process is the same across most cars: pop the case open, remove the old battery, note which side faced up, slide in a new one the same way, and close it. You can buy the replacement battery at any pharmacy, grocery store, or dollar store for less than the cost of a coffee.
Key Takeaways
- Most car key fobs use a CR2032, CR2025, or CR2016 battery — check your old battery or your owner's manual to know which one to buy.
- A flathead screwdriver or a coin works to pry open most key fobs; some fobs slide apart without tools.
- The battery has a + side and a − side — note which way it sits before you remove it, then install the new one the same way.
- If your key still does not work after you replace the battery, the problem is likely the circuit board or buttons, not the battery itself.
Identify your key fob type and battery size
Before you buy a battery, you need to know which one fits your key. Open your owner's manual and search for "key fob battery" or "remote battery" — it will list the exact model number. If you do not have the manual, look at the key fob itself. Most have a seam or slot that shows where it opens.
The three most common car key batteries are CR2032 (the largest), CR2025, and CR2016 (the smallest). If you cannot find the manual or read the fob, take the old battery to a pharmacy or electronics store and match it by size. Staff at these places see this every day and can tell you the right replacement in seconds.
Open your key fob without breaking it
Most key fobs open one of three ways: a slot you pry with a flathead screwdriver, a seam you slide apart by hand, or a screw you remove with a Phillips head screwdriver. Look at the edges of your fob. If you see a thin line running around the middle, that is a seam — try sliding your fingernail or a coin along it to separate the two halves.
If you see a slot or notch on the edge, use a flathead screwdriver or the edge of a coin to gently pry the case open. Start at one corner and work your way around — do not force it or you will crack the plastic. If you see a small screw, use a Phillips head screwdriver to remove it, then the case will come apart.
Once the fob is open, you will see the battery sitting in a small metal holder. It is a flat, round disc, usually silver or gold. Do not touch the circuit board or the rubber button pad more than you have to.
Remove the old battery and note its position
Before you take the old battery out, look at which side is facing up. The battery has a + symbol on one side and a − symbol on the other. Take a photo with your phone or write down which way it sits — this matters. If you install the new battery upside down, the key will not work.
Gently pry the battery out of its holder using a flathead screwdriver or your fingernail. The battery sits loosely in a metal clip, so it should come out easily. If it does not, do not force it — wiggle it gently side to side until it lifts free. Set the old battery aside.
Install the new battery the same way
Slide the new battery into the holder with the + side facing the same direction as the old one was facing. The metal clip on either side of the holder will hold it in place. You should hear or feel a small click as it seats. Do not press hard — if it does not slide in smoothly, you have it upside down.
Once the battery is in, close the key fob by pressing the two halves together until you hear a click. If your fob has a screw, replace it now. If it has a seam, slide the two halves together along the seam until they are flush. Test the buttons — lock and unlock your car a few times to make sure it works.
What to do if the key still does not work
If you installed a fresh battery and the key fob still does not lock or unlock your car, the problem is not the battery. The circuit board inside may be damaged, or the rubber button pad may have worn out. Water damage is also common — if your key has been wet, the circuit board may have corroded even if the battery is new.
At this point, you have two choices: buy a replacement key fob (usually $50 to $150 depending on your car) or take the key to a dealership and ask them to reprogram it or repair it. Some dealerships can fix water damage or replace the button pad for less than a new fob costs. Call ahead and ask what they charge for diagnosis.
Where to buy a replacement battery
Car key batteries are sold at pharmacies, grocery stores, dollar stores, and electronics retailers. CVS, Walgreens, Walmart, Target, and Best Buy all stock them. You can also order them online from Amazon or eBay for the same price or less. A single battery costs $3 to $10, and a pack of two or four costs only slightly more.
When you buy, bring the old battery with you or know the model number. Staff can match it by sight. If you buy the wrong size, most stores will exchange it for free — just keep your receipt.
Frequently Asked Questions
How long does a car key battery last?
Most car key batteries last three to four years with normal use. If you use your key fob many times a day, it may last two to three years. If you use it rarely, it could last five years or longer. There is no way to predict exactly when it will die — you will know when the buttons stop responding.
Can I replace the battery in a smart key or push-button start key?
Yes, the process is the same. Smart keys and push-button start keys have a battery inside that powers the remote lock and unlock functions. The battery compartment is usually hidden under a removable cover or behind a small door. Check your owner's manual for the exact location and battery type.
What if I install the battery upside down?
The key fob will not work at all. The circuit board needs the + side to face a specific direction. If you installed it and nothing happened, open the fob again and flip the battery 180 degrees. It should work when ready.
Do I need to reprogram my key after changing the battery?
No. Changing the battery does not erase the programming. Your key fob will work the same way it did before, as long as you install the new battery the correct way. Reprogramming is only needed if you buy a new key fob or if your car's locks have been changed.
Can I use any CR2032 battery, or does it have to be a specific brand?
Any CR2032 battery will work — the model number is the standard, not a brand name. Duracell, Energizer, Amazon Basics, and store brands all work the same way. Buy whichever is cheapest. The only difference between brands is how long they last, and most last long enough that you will not notice.