These instructions apply to the Mercedes CLA Mk2 (C118) 2019-Present. For other models, please choose your vehicle here.
Last updated:
A weak SmartKey is the usual reason a Mercedes-Benz CLA (C118, 2019–present) stops locking from a distance or shows a “key battery” warning. The fob takes a single CR2032 and you can change it in a couple of minutes.
Battery You Need
A CR2032 3 V coin cell. Fit it the same way up as the one you remove.
How to Replace the Key Battery
- Pull out the mechanical key blade from the back of the fob.
- Press the mechanical key against the cover to release it, and remove the cover.
- Use the key to press open the button-cell cover and lift it off — don’t bend the contact spring.
- Fit the new CR2032 positive (+) side up, keeping it free of grease.
- Refit the cell cover, the key cover and the mechanical key.
Lock and unlock from a few metres to confirm.
If It Still Won’t Work
- Start the car anyway — hold the SmartKey against the start button (or in the marked spot) as you press start.
- Lock manually with the emergency blade in the driver’s door (behind a small cap).
Frequently Asked Questions
What battery does the Mercedes CLA key take?
A CR2032 3 V coin cell, positive side up.
Do I need to reprogram the key after changing the battery?
No — it pairs again as soon as power is restored.
How do I open the SmartKey?
Pull out the mechanical blade, press it against the cover to release it, then use it to pop the cell cover.
My key still won’t start the car — what now?
Hold the SmartKey directly against the start button as you press it.
For a no-start with a warning light, check the code on autodtcs.com. See also our CLA battery guide if the car is dead.
Disclaimer: The information on this page is provided for general guidance only. Always follow your official service manual and safety precautions when working on your vehicle. We are not responsible for errors, omissions, or any damage resulting from the use of this information.
This website is an independent resource and is not affiliated with, endorsed by, or sponsored by Mercedes. All trademarks and brand names belong to their respective owners.