How to Replace a Mercedes-Benz Key Fob Battery

Quick answer: Most current Mercedes-Benz smart keys use a CR2025 3-volt coin battery. To change it, slide the release catch on the key, pull out the mechanical emergency key, use its tip to open the battery cover, swap the battery with the plus side facing the way the old one did, and close the cover. It takes about two minutes. Always check the size printed on the battery you remove, because older and some newer key designs can differ.

Signs your key battery is getting low

• A “Replace key battery” message in the instrument cluster
• You have to stand closer to the car for the buttons to work
• KEYLESS GO® (touching the door handle to unlock) works only some of the time
• The car does not detect the key when you press the start button

How to change the battery, step by step

1. Get the right battery. Buy a fresh CR2025 (or whatever is printed on your old one). Most pharmacies and grocery stores carry them.
2. Remove the emergency key. Slide the small release catch on the key fob and pull the metal emergency key out.
3. Open the battery cover. Insert the tip of the emergency key into the opening the key came from and gently press until the battery compartment releases.
4. Swap the battery. Note which side faces up, remove the old battery, and insert the new one the same way. Avoid touching the flat faces of the battery with your fingers.
5. Close everything up. Snap the cover back on and slide the emergency key back in until it clicks.
6. Test it. Lock and unlock the car with the buttons, then try KEYLESS GO® if your car has it.

Your owner’s manual shows the exact steps and pictures for your key. Here is how to access your owner’s manual on your phone.

What if the key battery dies completely?

You can still get in and drive. Use the metal emergency key to unlock the driver’s door (the lock cylinder may be hidden behind a cover on the handle). To start the car, hold the key fob against the marked spot on the steering column or center console, where the car can read the key without battery power, then press the start button. Your owner’s manual shows the exact spot for your model.

Use your phone as a backup key

Many newer models can use your phone as a Digital Vehicle Key, so a dead fob never strands you. Here is how to set up and use your Mercedes-Benz Digital Key.

When a new battery is not enough

If the key still does not work with a fresh battery, the key itself may be damaged, or you may need a spare. We can test the key, program a new one to your car, and order genuine replacements. See our page on Mercedes-Benz key replacement in Gilbert, or stop by our parts counter at 3455 S Gilbert Rd. Prefer we do it? Ask for a key battery check at your next service visit. Schedule service here or call (480) 407-5800.

Frequently asked questions

What battery does a Mercedes key fob take?

Most current Mercedes-Benz smart keys take a CR2025 3-volt coin battery. Check the size printed on the old battery to be sure.

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

No. Changing the battery does not erase the key. It should work as soon as the cover is closed.

How long does a Mercedes key battery last?

It depends on how often the key is used and whether it sits near the car, where KEYLESS GO® keeps it communicating. When the cluster shows a low battery message, replace it within a few weeks.