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How to Replace the Auxiliary Battery in a Mercedes-Benz S-Class W221

Model: Mercedes Classe S W221, MK 5 - Years 2005-2013
Part: Battery

In this video, you will see how to replace the auxiliary battery in a Mercedes-Benz S-Class W221. Like many high-end vehicles, the S-Class has an auxiliary battery that powers all its electronics. When you receive a message indicating a malfunction of the auxiliary battery, it means there is a low voltage issue, but it could also be due to faulty cables or relays. Before installing one of these batteries, it's best to test it with a voltmeter to ensure it has at least 12.6 volts. Then, remove the cover from the fuse compartment and take out the fuse panel; to do this, you will need to remove two screws and two bolts. Next, remove the four screws located under the dashboard to access the battery. Disconnect the negative terminal (black) first, then the positive terminal (red), and take the battery out of its bracket. Here, we will place the new battery, but first, we will test it. Connect the terminals, place it back in the bracket, and secure it in position. Reattach the lower part of the dashboard and then the fuse panel. Close the cover, and the operation is complete.

Updated on 24 July 2026 by ScegliAuto

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