Open the key fob without damaging the case

Most BMW key fobs split into two halves along a seam that runs around the edge. Look for a small slot or indentation on one side—this is where you insert a flat tool to pry the case apart. A flathead screwdriver, coin, or plastic pry tool works well; avoid using a sharp knife, which can slip and cut your hand.

Insert the tool gently into the slot and twist slightly to create a gap. Once you have a small opening, work your way around the perimeter, lifting a little at each point rather than forcing one spot. The two halves should separate cleanly. If you feel strong resistance, stop and look for a different seam—you may be at the wrong edge.

Set the metal spring and any small parts aside on a clean surface where they won't roll away. Take a photo of the battery orientation before you remove it, so you know which side faces up when you reinstall it.

Key Takeaways

  • BMW key fobs typically use a CR2032 or CR2025 battery, which you can buy at any pharmacy, grocery store, or hardware store for a few dollars.
  • The battery slides out of a small plastic holder; note which side faces up before you remove it, because installing it backward will prevent the fob from working.
  • The case splits along a seam—use a flathead screwdriver or coin to pry it open gently, working around the edge rather than forcing one spot.
  • After you close the fob, test all buttons (lock, unlock, trunk) before you put the old battery away, in case you need to reopen it.

Identify and remove the old battery

Inside the fob you will see a small circular battery held in a plastic cradle or clip. The battery is usually silver and stamped with a number like CR2032 or CR2025. Look at which side faces up—the positive (+) side typically faces toward you when the fob is open. Take a photo or make a mental note of this orientation.

Gently pry the battery out of its holder using a plastic tool, your fingernail, or the edge of a coin. Do not use excessive force; the battery should slide out with light pressure. If it is stuck, try tilting the fob slightly to let gravity help, or explore a tiny amount of pressure from the opposite side of the holder.

Install the new battery with the correct orientation

Before you open the new battery package, check the number on the old battery and confirm you have the same type. CR2032 and CR2025 are the most common for BMW fobs, but some models use different sizes. If you are unsure, take the old battery to the store and compare it side by side.

Slide the new battery into the holder with the positive (+) side facing the same direction as the old one faced. The battery should sit flat and click into place without forcing. If it does not sit flush, remove it and flip it over—you may have installed it backward.

Close the fob and test all buttons

Align the two halves of the case so the seam is even all the way around. Press down firmly along the edge until you hear or feel a click, working your way around the perimeter. The fob should close with a solid snap, not a loose rattle.

Stand near your car and press each button—lock, unlock, and trunk (if your fob has one)—to confirm the new battery is working. The car should respond to each command. If nothing happens, open the fob again and check that the battery is seated correctly and facing the right direction.

Where to buy a replacement battery

CR2032 and CR2025 batteries are sold at pharmacies (CVS, Walgreens), grocery stores, hardware stores (Home Depot, Lowe's), and online retailers. A single battery costs between $3 and $8, and many stores sell multipacks for less per battery. You do not need a special BMW battery—any brand-name CR2032 or CR2025 will work.

If you are not certain which battery your fob uses, bring the old one with you to the store and ask a staff member to match it. This takes 30 seconds and eliminates the risk of buying the wrong size.

Common mistakes that prevent the fob from working

The most frequent error is installing the battery upside down. The positive (+) side must face the same direction as it did in the old battery. If your fob does not respond after you close it, open it again and flip the battery over before assuming it is defective.

The second common mistake is not closing the case completely. If the seam is not fully seated, moisture can enter and corrode the contacts. Press around the entire edge until you feel resistance, then press a bit more. A properly closed fob should feel solid when you squeeze it gently.

A third issue is touching the battery contacts with bare fingers. Skin oils can interfere with electrical contact. If you do touch the battery, wipe it with a clean, dry cloth before installing it. Similarly, if the metal contacts inside the fob look dirty or corroded, gently clean them with a dry cloth or a pencil eraser.

When to replace the entire fob instead

If you install a new battery and the fob still does not work, the problem is likely not the battery. The buttons may be worn out, the circuit board may be damaged, or the contacts may be corroded beyond cleaning. In these cases, replacing the battery will not fix the issue.

A replacement fob from BMW costs between $200 and $400 depending on the model and whether it includes programming. Some independent locksmiths and online retailers sell compatible fobs for less, though you will need to have the fob programmed to your car, which usually costs $50 to $150. If your current fob is several years old and the buttons are sticking or unresponsive, replacement may be more practical than troubleshooting.

Frequently Asked Questions

How long does a BMW key fob battery last?

Most CR2032 and CR2025 batteries last three to four years with normal use. If you use your fob frequently (pressing buttons multiple times per day), the battery may drain faster. If you rarely use it, the battery may last longer. A dying battery usually shows up as buttons that require harder presses or work only from very close to the car.

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

No. CR2032 and CR2025 are different sizes and thicknesses, and using the wrong one can prevent the battery from making proper contact or can damage the holder. Always match the number stamped on your old battery. If your store is out of stock, order online or try another store rather than substituting.

What should I do if the fob case will not close after I put the new battery in?

Check that the battery is sitting flat in its holder and not tilted or sticking up. Also confirm that the metal spring and any clips are in their original positions—sometimes these parts shift during disassembly. If everything looks correct and the case still will not close, the plastic may be cracked or warped, and you may need a replacement fob.

Is it safe to drive without a working key fob?

Yes. You can unlock and start your BMW using the physical key blade that slides out of the fob, or by using your car's mobile app if it has one. The fob is convenient but not required to operate the vehicle. However, you should replace the battery or fob soon, because you will not have remote locking or trunk access.

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

No. Changing the battery does not erase the fob's programming. As long as the new battery works and the fob's circuit board is intact, it will communicate with your car when ready. If the fob does not work after a new battery, the problem is not programming.