Replacing the key battery
DANGER Risk of fatal injury due to swallowing batteries
Batteries contain toxic and corrosive substances. If batteries are swallowed or otherwise enter the body, severe internal burns can occur within two hours.
There is a risk of fatal injury!
Keep the batteries out of the reach of children.
If the battery cover does not close securely, stop using the key and keep it away from children.
If batteries are swallowed or otherwise enter the body, seek immediate medical attention.
ENVIRONMENTAL NOTE Environmental damage due to improper disposal of batteries
Batteries contain pollutants. It is illegal to dispose of them with the household rubbish.
Dispose of batteries in an environmentally responsible manner. Take discharged batteries to a qualified specialist workshop or to a collection point for used batteries. Requirements:
You need one CR 2025 3 V cell battery
Replacing the battery
Mercedes-Benz recommends that you have the battery changed at a qualified specialist workshop.
Remove the emergency key More.
Press emergency key 
into the opening in the key in the direction of the arrow until battery compartment cover 
opens. When doing so, do not hold battery compartment cover shut.
into the opening in the key in the direction of the arrow until battery compartment cover opens. When doing so, do not hold battery compartment cover shut. Tap the key against the palm of your hand so that battery 
falls out of the battery compartment.
falls out of the battery compartment. Insert the new battery into the battery tray with the positive pole facing upwards. Use a lint-free cloth to do so.
Fit battery compartment cover to the key casing with the front lugs first and push it closed.
to the key casing with the front lugs first and push it closed. Slide emergency key back into the key More.
back into the key More.