How to Change the Battery in the Key of a C280 Mercedes

1. Pull out the mechanical key located inside the Smart Key housing by pushing the small lever next to the keychain ring.
2. 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.
3. 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.
4. 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.