Most car key batteries are coin-cell batteries you can swap yourself in under a minute

Your car key battery is almost certainly a small coin-shaped battery — usually a CR2032, CR2025, or CR2016 — that you can buy at any drugstore or supermarket for two to five dollars. The battery sits inside the plastic fob, and you can reach it by prying the fob open with a coin or flathead screwdriver. Once you have the fob apart, you slide out the old battery, note which side was facing up, and slide in the new one the same way. The whole job takes longer to describe than to do.

The tricky part is not the battery swap — it is knowing which battery your key takes and whether your fob is designed to open. Some newer luxury cars use proprietary batteries or sealed fobs that require a dealer visit. Most cars made in the last 20 years, though, use a standard battery and a fob you can open yourself.

Key Takeaways

  • Your car key battery is a coin-cell battery (usually CR2032, CR2025, or CR2016) that costs two to five dollars and lasts three to four years.
  • You can open most fobs by inserting a coin or flathead screwdriver into the seam and twisting gently until the two halves separate.
  • When you install the new battery, the flat side (marked with a + or −) must face the same direction as the old one did.
  • If your fob does not open or your car is a luxury brand, contact your dealer — some fobs are sealed or use proprietary batteries.
  • A dying key battery shows up as a button that works only when pressed hard, or a range that shrinks to a few feet from the car.

How to identify which battery your key takes

The easiest way is to look at your owner's manual, which usually lists the battery type in the key fob section. If you do not have the manual, search your car's year, make, and model plus "key fob battery" online — you will find the answer in seconds on forums or parts sites.

If you want to know without opening the fob, call your car's dealer with your vehicle identification number (VIN) and they will tell you the battery type. You do not need to buy it from them; any pharmacy or electronics store carries standard coin-cell batteries.

Once you know the type, buy a fresh battery before you open the fob. Coin-cell batteries are cheap enough that there is no reason to reuse an old one or guess at a substitute.

Opening the fob without breaking it

Most car key fobs have a seam running around the edge where the two plastic halves meet. Insert a coin (a dime or penny works) or a flathead screwdriver into that seam and twist gently. You are not trying to pry it apart — you are explore rotational pressure to separate the halves. Start at one corner and work your way around if the first spot does not budge.

Some fobs have a small slot or notch on one edge instead of a full seam. If you see that, insert your coin or screwdriver into the slot and twist. The fob should pop open without much force. If you are straining hard, you may have the wrong angle — try a different spot on the seam.

Once the fob is open, you will see the battery sitting in a small metal or plastic holder. It is usually held in place by nothing more than gravity, so it will slide out easily when you tilt the fob.

Removing the old battery and installing the new one

Before you touch the old battery, look at which side is facing up. Coin-cell batteries have a flat side (marked with a + or −) and a domed side. The marking tells you the polarity — which way the battery must sit for the fob to work. Write down or remember which side was up, or take a photo.

Slide the old battery out of its holder. If it is stuck, use a plastic spoon or the edge of a credit card to gently pry it up — do not use a metal tool that could short the battery or damage the holder.

Slide the new battery into the holder with the same side facing up as the old one. It should sit flat and snug. Do not force it; if it does not slide in smoothly, you may have the polarity backwards. Flip it and try again.

Closing the fob and testing the key

Once the battery is in place, press the two halves of the fob back together. You should hear or feel a small click as they snap into place. If they do not close flush, the battery may be sitting wrong — open it again and check that it is fully seated in the holder.

Test the key by standing a few feet from your car and pressing the lock and unlock buttons. The car should respond normally. If the buttons do not work, open the fob again and check that the battery is installed with the correct polarity. If it is, the battery may be defective — swap it for a fresh one from a different package.

If the fob still does not work after you have tried a new battery with the correct polarity, the problem is likely inside the fob itself (a broken button contact or circuit board) rather than the battery. At that point, contact your dealer about a replacement fob.

When to call the dealer instead

Some car manufacturers, especially luxury brands like BMW, Mercedes, and Audi, use sealed fobs that are not designed to open. If your fob has no visible seam and does not have a slot, do not force it — you will break the plastic. Contact your dealer instead.

A few high-end vehicles also use proprietary batteries that are not standard coin cells. Your dealer can tell you whether that applies to your car. If it does, you will need to buy the battery from them or have them install it.

If your car is under warranty and the key fob is failing, the dealer may replace it at no cost. It is worth asking before you buy a new battery.

Signs your key battery is dying

A failing key battery usually shows up as a button that only works when you press it hard, or a range that shrinks — you have to stand closer to the car for the unlock button to work. Some people notice the button feels mushy or requires more pressure than it used to.

If only one button works and the others do not, the problem is probably not the battery — it is a broken button contact inside the fob. A battery replacement will not fix that.

Key batteries typically last three to four years, depending on how often you use the fob. If your battery is older than that and the fob is acting sluggish, a fresh battery will almost certainly solve it.

Frequently Asked Questions

Can I use a different battery type if I cannot find the exact one?

No. Coin-cell batteries come in different sizes and voltages, and using the wrong one can damage the fob or not work at all. The correct battery type is specific to your key. If you cannot find it locally, order it online — it will arrive in a day or two.

What do I do with the old battery?

Coin-cell batteries contain small amounts of lithium or mercury and should not go in the trash. Most pharmacies and electronics stores have battery recycling bins near the checkout. Drop the old battery there on your way out.

Will replacing the battery erase my car's memory or settings?

No. The key fob battery is separate from your car's computer. Swapping it will not affect any settings, programming, or stored information in your vehicle.

How do I know if the fob is broken versus the battery being dead?

Install a fresh battery first. If the fob works normally after that, the battery was the problem. If it still does not work, or if only some buttons work, the fob itself is likely damaged and needs replacement.

Can I buy a universal key fob instead of replacing the battery?

Universal fobs exist, but they require programming to your car and are more expensive than a battery replacement. Try the battery first — it solves the problem nine times out of ten.