The Mercedes-Benz C280 was manufactured from 1993 to 2008 and features a naturally aspirated 2.8-liter in-line-six power plant. The C280 also featured an electronic "Smart Key" that enables the driver to gain access to the vehicle and turn the engine on or off. While the Smart Key features an integrated mechanical key for emergencies, you may wish to replace the dead or failing batteries located inside your Smart Key to restore the electronic functions.
Pull out the mechanical key located inside the Smart Key housing by pushing the small lever next to the keychain ring.
Examine the slot that contains the mechanical key for a small lever, inside the Smart Key housing. Use the end of the mechanical key to push in the small lever, holding the top portion of the battery holder inside the Smart Key housing.
Separate the top and bottom portions of the Smart Key housing in order to pull out the battery holder. Slide the two quarter-size batteries out of the battery holder. Make note of the old battery orientation and insert the new batteries into the holder in the same manner.
Insert the battery holder into the Smart Key housing. Make sure the battery holder has locked into place by trying to separate the battery holder from the Smart Key housing. Reinsert the mechanical key into the proper slot inside the Smart Key housing to complete the process.
