The most common key fob batteries are CR2032, CR2025, and CR2016

The battery size your key fob needs depends on the make and model of your car, not the fob itself. A CR2032 is the most common size across all manufacturers — it powers fobs for Toyota, Honda, Ford, BMW, and most others. The CR2025 and CR2016 are thinner alternatives that fit in some compact fobs, but they hold less charge and drain faster.

The easiest way to find your fob's battery size is to open it and look at the old battery. The size is printed directly on the metal disc — you will see "CR" followed by four numbers. Write that number down before you go to the store, or take a photo of the battery itself.

If you have lost the old battery or cannot open the fob, check your vehicle's owner's manual. The manual lists the battery type in the key fob section, usually near the back. You can also call your car's dealership with your vehicle identification number (VIN) — they will tell you the correct size in one call.

Key Takeaways

  • CR2032 is the standard battery for most car key fobs across all major manufacturers.
  • The battery size is printed on the old battery itself, so opening your fob is the fastest way to find out what you need.
  • CR2025 and CR2016 are smaller alternatives used in compact fobs, but they do not last as long as CR2032.
  • Your vehicle's owner's manual or dealership can confirm the correct size if you cannot access the old battery.

How to open your key fob safely

Most key fobs split in half along a seam. Look for a thin line running around the edge of the fob — that is where the two halves meet. Slide a flat tool like a butter knife or coin into the seam and gently twist to pry the halves apart. Do not force it; if it does not budge after light pressure, you may be pushing in the wrong spot.

Once the fob is open, the battery sits in a small metal holder. Note which side faces up — the flat side or the raised side with the plus sign. When you install the new battery, it must face the same direction. Take a photo before you remove the old battery so you remember the orientation.

Some fobs have a small plastic tab under the battery. This tab keeps the battery from touching the contacts during shipping. If your new battery has this tab, pull it out gently before closing the fob. If you forget, the fob will not work.

Why battery size matters

The numbers in the battery code tell you the physical dimensions. A CR2032 is 20 millimeters wide and 3.2 millimeters thick. A CR2025 is the same width but only 2.5 millimeters thick. A CR2016 is 16 millimeters wide and 1.6 millimeters thick. If you buy a battery that is too thick, it will not fit inside the fob. If you buy one that is too thin, it will rattle and may lose contact with the metal holder.

The last two digits also tell you the voltage and chemistry. All three sizes (CR2032, CR2025, CR2016) are 3-volt lithium batteries, so they work the same way — the difference is only how long they last. A CR2032 typically lasts three to four years in a key fob. A CR2025 lasts two to three years. A CR2016 lasts one to two years because it holds less energy.

Where to buy the right battery

You can find CR2032, CR2025, and CR2016 batteries at any pharmacy, grocery store, hardware store, or online retailer. They cost between 50 cents and two dollars each, depending on the brand. Duracell, Energizer, and Panasonic are reliable brands that you will find everywhere. Store-brand batteries work just as well and cost less.

Buy a single battery first, not a pack of ten. Key fob batteries last years, and you will not need a backup for a long time. If you buy in bulk and do not use them, they will sit in a drawer and lose their charge before you need them.

Some car dealerships sell batteries, but they charge two to three times the retail price. Unless you are already at the dealership for service, it is not worth the trip.

Installing the new battery correctly

Wash your hands before you touch the new battery. Oils from your skin can leave a film on the metal contacts, which weakens the connection. If you have already touched the battery, wipe it gently with a dry cloth.

Drop the new battery into the holder with the correct side facing up — the side that was facing up in the old battery. Press down gently until you hear or feel a small click. The battery should sit flat and not rock side to side. If it rocks, remove it and check that the holder is clean and free of debris.

Close the fob by pressing the two halves together firmly until they snap. You should hear a click. Test the fob by pressing each button and watching your car's lights blink or hearing it lock and unlock. If nothing happens, open the fob again and check that the battery is seated correctly and facing the right direction.

What to do if the fob still does not work

If you installed a new battery and the fob still does not respond, the problem is usually not the battery. The metal contacts inside the fob may be corroded or dirty. Open the fob again and look at the two metal circles where the battery touches. If they look dark or discolored, rub them gently with a pencil eraser or a dry cloth to remove the corrosion.

If the contacts look clean and the fob still does not work, the circuit board inside may be damaged. This happens if the fob was dropped, sat in water, or is very old. In this case, you will need a replacement fob from your car's dealership or an aftermarket supplier.

Before you buy a new fob, test the battery in another device that uses the same size — a remote control, a thermometer, or a scale. If the battery works in another device, the fob itself is the problem. If the battery does not work in any device, you may have bought a dead battery by accident, and you should return it to the store.

Frequently Asked Questions

Can I use a different size battery if my fob is too small for CR2032?

No. If your fob is designed for CR2025 or CR2016, you must use that size. A larger battery will not fit, and a smaller battery will not make proper contact with the holder. Always match the size printed on your old battery.

How long does a key fob battery last?

A CR2032 typically lasts three to four years with normal use — pressing the buttons a few times per day. If you use your fob constantly or live in a very cold climate, it may drain faster. A CR2025 lasts two to three years, and a CR2016 lasts one to two years.

What if I cannot get the fob open?

Try a different tool — a flathead screwdriver, a plastic spoon, or a coin. Look for the seam again and make sure you are pushing in the right spot. If the fob is stuck, do not force it; take it to a car dealership or a locksmith, and they will open it for you for a small fee.

Is it safe to use rechargeable batteries in a key fob?

No. Rechargeable batteries have a different voltage and chemistry than single-use lithium batteries. They will not power a key fob reliably and may damage the circuit board. Always use a fresh CR2032, CR2025, or CR2016 battery.

Do I need to reprogram my key fob after changing the battery?

No. Changing the battery does not erase the fob's programming. It will work when ready after you install the new battery and close the fob. If it does not work, the problem is the battery installation or the fob itself, not the programming.