In Mercedes-Benz’s C-Class Saloon owner’s manual (UK edition), the key runs on a CR 2032 coin cell. For another Mercedes-Benz model, check the code on the old battery.
The battery it takes
Mercedes-Benz’s C-Class Saloon owner’s manual (UK edition) says the key needs a CR 2032 lithium cell battery (3 V).
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How to change it, in Mercedes-Benz’s steps
Mercedes-Benz recommends having the battery replaced at a qualified specialist workshop. The manual’s own steps:
- Press the release knob and pull the emergency key fully out.
- Press the emergency key into the opening in the key, the way the arrow points, until the cover opens. Don’t press down on the cover.
- Put the emergency key into the opening to unclip the second cover, and take it off.
- Tap the key against your palm until the battery drops out.
- Fit the new battery positive terminal up, using a lint-free cloth, and check that its surface is free from lint, grease and other dirt.
- Put each cover back front tabs first and press down until it’s completely closed, then push the emergency key back in until it engages.
Checking the key battery
If the key’s indicator lamp doesn’t light when you press its lock or unlock button, the battery is low or may be completely flat, and the manual says to replace it as soon as possible. The driver display can also show Change key batteries when the key battery is discharged.
When you can no longer lock or unlock the car, a low or flat key battery is one possible cause. Besides a new battery, the manual’s remedies include the replacement key and locking or unlocking with the emergency key.
If the car doesn’t start with the key
When the driver display says Place the key in the marked space, the car can start in emergency operation mode. Empty the storage compartment, take the key off its key ring and place it on the symbol in the storage compartment, and the car starts after a short delay. If it doesn’t, leave the key there, press the brake pedal and use the start/stop button. Mercedes-Benz also says to have the key checked at a qualified specialist workshop.
Keep coin batteries away from children
Mercedes-Benz warns that a swallowed battery can cause severe internal burns within two hours, with a risk of fatal injury. If the battery compartment cover or lid doesn’t close securely, stop using the key and keep it away from children. Its manual adds a warning not to expose batteries to high temperatures, such as long spells in sunlight, as they can give off flammable gas and explode.
The National Capital Poison Center says that if anyone swallows a battery, immediately call the 24-hour National Battery Ingestion Hotline at 1-800-498-8666 or your poison center at 1-800-222-1222. Don’t delay. Immediate treatment decreases severity.