Most key fobs use coin-cell batteries, usually CR2032 or CR2025

The battery in your key fob is almost certainly a coin-cell battery — a flat, round battery about the size of a dime. The most common type is the CR2032, which is 20 millimetres across and 3.2 millimetres thick. The second most common is the CR2025, which is the same width but slightly thinner at 2.5 millimetres. Both are lithium batteries that cost between $3 and $8 for a single battery at a drugstore or supermarket.

Some older or luxury car fobs use CR2016 (thinner still) or CR2430 (thicker and higher capacity). A few fobs use AAA or AA batteries instead, though this is less common in modern cars. The easiest way to know which one your fob needs is to open it and look at the battery itself — the type is printed on the metal casing.

Key Takeaways

  • CR2032 is the standard battery for most car key fobs sold in the last 20 years.
  • The battery type is printed directly on the battery casing, so you can check before you buy a replacement.
  • Coin-cell batteries cost $3 to $8 each and are sold at pharmacies, supermarkets, and hardware stores.
  • Some fobs use CR2025, CR2016, or CR2430 instead, and a few older models use AA or AAA batteries.
  • You can replace the battery yourself in most fobs by prying open the case with a coin or small flathead screwdriver.

How to identify your fob's battery without opening it

If you do not want to open the fob yet, check your owner's manual or the manufacturer's website. Search for your car's year, make, and model plus "key fob battery" — most manufacturers list the battery type on a support page. You can also call your car's dealership service department and give them your vehicle identification number (VIN); they will tell you the battery type in under a minute.

If you have lost the manual and cannot reach the dealership, take the fob to any pharmacy or supermarket with a battery section. Staff there can usually open it for you and tell you the type, or you can open it yourself with a coin. Once you see the battery, the type is right there on the metal surface.

CR2032 vs. CR2025 and other common types

The CR2032 and CR2025 are not interchangeable, though they look nearly identical. The CR2032 is thicker and holds more charge, so it lasts longer — typically 3 to 4 years in a fob you use daily. The CR2025 lasts about 2 to 3 years. If you put a CR2025 in a fob designed for CR2032, it will work at first but may not fit snugly, and the fob may not function reliably.

The CR2016 is thinner than both and is used in some slim fobs, particularly older models. The CR2430 is thicker and holds more charge, used in fobs that are used very frequently or in vehicles with longer-range remotes. Always use the exact type your fob is designed for — using the wrong size can damage the battery contacts or cause the fob to malfunction.

Where to buy replacement batteries

Coin-cell batteries are sold everywhere: pharmacies (CVS, Walgreens), supermarkets (Walmart, Target, grocery chains), hardware stores (Home Depot, Lowe's), and online (Amazon, eBay). A single CR2032 costs $3 to $8 depending on the brand and where you buy it. Name brands like Energizer and Duracell cost more than store brands, but they all perform similarly in a key fob.

Some car dealerships sell key fob batteries, but they charge a markup — often $10 to $15 for the same battery you can buy for $4 elsewhere. If the dealership offers to replace the battery for you, the service charge is usually $20 to $50 on top of the battery cost. For most people, buying the battery yourself and replacing it takes 30 seconds and costs far less.

How to replace the battery yourself

Open the fob by inserting a coin (a quarter works well) or a small flathead screwdriver into the seam between the two halves. Twist gently until the case pops open — do not force it or you may crack the plastic. Once open, note which side of the battery is facing up (the + or − symbol), then lift out the old battery with your fingernail or a plastic tool.

Drop the new battery in with the same side facing up as the old one. Close the case by pressing the two halves together until they click. Test the fob by pressing a button — if it works, you are done. If it does not work, open it again and check that the battery is seated properly and facing the right direction.

Signs your key fob battery is dying

The first sign is that you have to press the button harder or multiple times to get the fob to work. The range also shrinks — you may have to stand closer to the car for the lock or unlock button to register. Some fobs will work from across a parking lot when the battery is fresh but only from a few feet away when it is dying.

Eventually the fob will stop working entirely. This usually happens suddenly rather than gradually, because the voltage drops below the threshold the fob's circuit needs to transmit a signal. Once this happens, replacing the battery is the only fix. If the fob still does not work after you replace the battery, the problem is likely a broken button contact or a dead circuit board, not the battery.

Frequently Asked Questions

Can I use a CR2025 in a fob that takes CR2032?

Technically it will work at first, but it is not recommended. The CR2025 is thinner and may not make reliable contact with the battery terminals. Over time the connection can become loose, causing the fob to work intermittently. Use the correct battery type to avoid this problem.

How long does a key fob battery last?

A CR2032 in a fob you use daily typically lasts 3 to 4 years. If you use the fob less often, it can last 5 years or longer. The battery will eventually die even if you do not use it, because lithium batteries self-discharge slowly over time.

What if my fob uses a rechargeable battery?

Some luxury car fobs have rechargeable batteries built in. These usually charge through a USB port on the fob itself. Check your owner's manual to see if your fob is rechargeable. If it is, you will not need to buy replacement batteries, but the charging port can wear out over time.

Is it safe to replace the battery myself?

Yes. Coin-cell batteries are safe to handle with your bare hands. The only precaution is to keep them away from small children and pets, since swallowing one can cause internal burns. Wash your hands after handling the battery, and do not leave old batteries lying around.

Why is my new battery not working?

The most common reason is that the battery is installed backwards — the + side should face up. Open the fob and check the orientation. If it is correct and the fob still does not work, the battery terminals may be dirty. Try cleaning them with a dry cloth, or the fob's circuit board may be damaged and need professional repair.