You can replace the battery yourself in about two minutes with a coin
The battery in your BMW 3 Series key fob dies like any other battery—usually after three to four years of regular use. You do not need to visit a dealer. The whole job takes a coin, a replacement battery (CR2032, which costs a few dollars at any pharmacy or hardware store), and two minutes of your time.
The process is the same whether you have a newer fob with a flip key or an older one with a fixed key. The battery compartment is on the back of the fob, and BMW designed it so you can open it without tools.
Key Takeaways
- BMW 3 Series key fobs use a CR2032 battery, which you can buy at any drugstore, supermarket, or hardware store for a few dollars.
- The battery compartment opens by sliding a coin into the slot on the back of the fob and twisting gently—no screwdriver needed.
- When you insert the new battery, the flat side faces up and the rounded side faces down toward the spring.
- After you close the fob, test the lock and unlock buttons to confirm the new battery is working before you put the key away.
What you need before you start
Gather these items before you open the fob: a CR2032 replacement battery, a coin (a dime or penny works), and a clean, flat surface to work on so you do not lose the small spring inside.
The CR2032 is a standard coin-cell battery. You will find it in the pharmacy section, the electronics aisle, or the checkout area of most drugstores and supermarkets. Some hardware stores and big-box retailers stock them as well. The battery usually costs between $2 and $5 for a single unit, though multi-packs are cheaper per battery if you want spares.
How to open the fob and remove the old battery
Turn the key fob over so the back is facing you. You will see a small horizontal slot near the edge of the fob—this is where the coin goes. Insert the edge of your coin (a dime or penny) into the slot and twist gently, as if you were opening a jar lid. The slot is designed to let you explore leverage without damaging the plastic.
The back cover will pop off or slide out slightly. Once there is enough space, use your fingers to pull the cover the rest of the way off. Inside, you will see the old battery sitting on top of a small metal spring. The battery is round and flat, about the size of a dime.
Lift the old battery straight up and out. If it is stuck, a gentle wiggle usually frees it. Set it aside—you do not need it anymore. Do not lose the spring underneath; you will need it when you put the new battery in.
Installing the new battery the right way
Before you insert the new CR2032, check which side faces which direction. The battery has a flat side and a rounded side. The flat side should face up (toward you, away from the fob body), and the rounded side should face down (toward the spring inside the fob).
Place the new battery on top of the spring, rounded side down, and press gently until it sits flat. You should hear or feel a small click as it settles into place. Do not force it; if it does not sit easily, lift it and check that the spring is not bent or folded.
Closing the fob and testing the buttons
Slide the back cover back onto the fob. It should fit snugly and sit flush with the rest of the plastic. If it does not close all the way, lift the cover and check that the battery is sitting flat and the spring is not sticking up.
Once the cover is closed, press the lock button and the unlock button a few times. You should hear the car respond—the doors will lock and unlock, or you will see the lights flash. If nothing happens, open the fob again and check that the battery is seated correctly and facing the right direction.
When to replace the battery again
A new CR2032 battery typically lasts three to four years in a BMW key fob, depending on how often you use it. You will know it is time to replace it when the buttons stop responding or respond only when you press them very hard. Some newer BMW models will show a low-battery warning on the dashboard, but not all do.
Keep a spare CR2032 in a drawer at home so you are not caught without a working key fob. The battery is cheap and lasts indefinitely in storage, so there is no downside to having a backup.
When to call a BMW dealer instead
If you open the fob and the battery compartment looks different than described here, or if the cover will not open with a coin, you may have an older or unusual model. Stop and contact a BMW dealer or a local locksmith who works on BMW keys. Do not force the cover; you can crack the plastic.
If you replace the battery and the fob still does not work, the problem is not the battery. The circuit board or buttons inside may be damaged, or the fob may have gotten wet. A dealer can diagnose this, though repair or replacement is usually more expensive than buying a new fob from a third-party supplier.
Frequently Asked Questions
Can I use a different battery size instead of CR2032?
No. The CR2032 is the correct size for BMW 3 Series fobs, and other batteries will not fit or work. Do not try to use a CR2025 or CR2016, even though they look similar. The fob is designed for the CR2032 specifically.
What if I lose the spring when I open the fob?
The spring is small but important—it holds the battery in place and completes the electrical circuit. If you lose it, you can order a replacement spring from BMW or a third-party key fob supplier, or you can buy a whole new fob. A replacement spring costs a few dollars if you can find one separately.
Does the fob need to be reprogrammed after I change the battery?
No. Changing the battery does not erase the fob's programming. Once you close the cover and the new battery is in place, the fob should work when ready without any additional steps.
How do I know if the battery is installed upside down?
If the fob does not respond when you press the buttons, open it again and check the battery direction. The flat side should face up toward you, and the rounded side should face down toward the spring. Flip it if it is backwards, close the fob, and test again.