Replacing the Auxiliary Battery of the Mercedes-Benz

2010+ Mercedes-Benz S CL Class W221 Auxiliary Battery Replacement

The most common symptom of a faulty auxiliary battery is a warning message on the dashboard displaying: Auxiliary Battery Malfunction. The early 2006 and 2007 S-Class models have two batteries but no auxiliary battery under the dash. One battery is behind the rear seats; the second battery is in the engine bay.

This guide also applies to CL-Class W216 from 2007 to 2013. Applicable to models such as CL550 CL63 AMG.

What you will need

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  • 10mm wrench
  • Torx Socket Set
  • Dashboard Trim Removal Tool


  1. Disconnect the negative battery from the main battery. The main battery will be on the engine bay, passenger side, or behind the rear seat (accessible through the trunk).
  2. Remove the plastic cover on the driver’s side of the dashboard using a dash removal trim. open side cover access mercedes aux battery in dashboard
  3. Remove two Torx screws that hold the fuse box in place. Pull the fuse box out but do not unplug the electrical connector. remove fuse box to access aux battery
  4. Remove the 10mm bolts that hold the auxiliary battery bracket in place. s550 aux battery bolt bracket removal
  5. Remove the auxiliary battery from the bracket. Next, unplug the negative and positive wires from the auxiliary battery. remove mercedes s class w221 auxiliary battery
  6. Install the auxiliary battery in reverse order. mercedes s class auxiliary battery replacement

There is very little space in the dash, so removing the auxiliary battery may be difficult. If that is the case, remove the panel from under the dashboard. This will allow you to access the auxiliary battery from under the dashboard.

Once you replace the auxiliary battery, the Auxilary Battery Malfunction on the dashboard should turn off immediately. Unless the auxiliary battery is not charged, it may take a few driving cycles for the instrument cluster error message to turn off.

We hope you find the 2008-2013 Mercedes S CL Class W221 Auxiliary Battery Replacement guide helpful. Check these troubleshooting and repair guides for more help on your Mercedes-Benz.


  • Rushit Hila • ASE Certified

    Rushit Hila, an ASE-certified engineer (G1 Automotive Maintenance and Repair), brings over two decades of hands-on experience in the automotive world to his writing. With a strong educational background, including a Master of Science in Engineering and a Bachelor of Science in Engineering, he has honed his skills and expertise through years of practical work. As a respected authority in the field, Mr. Hila is dedicated to offering insightful and valuable content that resonates with both vehicle owners and mechanics.

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One Comment

  1. Anonymous says:

    2007 s550 4matic DOES NOT have a aux battery in the dash.