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 lid and/or the battery compartment do 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:
a CR 2032 3 V cell battery
Mercedes-Benz recommends that you have the battery replaced by a qualified specialist workshop.
Remove the emergency key More.
Example image
Press release button 
down fully and slide cover 
forward.
down fully and slide cover forward. Remove battery compartment 
and remove the discharged battery.
and remove the discharged battery. Insert the new battery into battery compartment . Observe the positive pole marking in the battery compartment and on the battery.
. Observe the positive pole marking in the battery compartment and on the battery. Insert battery compartment .
. Replace cover so that it engages.
so that it engages. Slide the emergency key in completely until it engages More.