The Mercedes C240 was part of the Mercedes C-Class line through the 2007 model year. Since the C240 includes a maintenance-free battery, it is unlikely you will need to remove the battery until it is due for replacement, typically every three to five years. You can buy a replacement battery from an auto parts retailer or Mercedes-Benz dealer and change it at home in minutes.
Turn off the ignition and any accessories inside the car. Remove the key to avoid accidental starting. Open the bonnet.
Lift the three clamps on the back of the battery filter box on the passenger side of the engine compartment. Remove the filter box cover to expose the battery.
Disconnect the negative cable with a wrench. Repeat the process for the positive cable. Remove the retaining nuts on the battery with a wrench. Lift the battery out of the battery tray.
Insert the new battery into the tray in the same alignment as the one you removed. Secure the battery with the retaining nuts, tightening them with a wrench.
Reconnect the positive cable and tighten it using the wrench. Repeat the process for the negative cable. Replace the filter cover and press the clamps down to lock it in place. Close the bonnet and start the engine to test the new battery.