Instructions and videos on this guide show you how to replace the onboard electrical system battery in 2006, 2007, 2008, 2009 Mercedes-Benz S-Class S550 S400 (W221), and CL (W216) vehicles.

This is known as the onboard electrical system battery or G1 battery. This is not the starter battery. 

The W221  vehicles have two batteries.  One is under the hood (known as the starter battery), and the one that we show in this guide, located behind the rear seat.

It is important to note that 2009 and newer models no longer have this battery behind the rear seat. For 2009 and newer models (except the S400 hybrid), the main battery is located in the engine bay. A smaller auxiliary battery is installed under the dashboard on the driver's side. 

What you will need


  1. Park your Mercedes-Benz S-Class and press the parking button on the dashboard. 
  2. Open the trunk and access the panel behind the rear seat. MERCEDES BATTERY BEHIND REAR SEAT


  3. Remove the panel by pulling it towards the back of the car. This will expose the battery behind the rear seat. 
  4. Disconnect the negative battery terminal. 
  5. Disconnect the positive battery terminal. 
  6. Remove the 13mm bolt to remove the bracket that holds the battery. REMOVE 13MM BOLT


  7. Remove the battery by sliding it towards the back. 
  8. Install the new battery in reverse order. The negative battery terminal should be the last thing that you need to connect. 

Saving the memory settings

It is possible to retain all the memory and settings by connecting a secondary battery source. For this purpose, you will need to use a 12-volt trickle charger.

The external source can be connected to the positive post located on the engine bay's passenger side. 


If you decide to use an external energy source to keep the car powered up, you need to be extremely careful not to short the positive terminal to the vehicle's body. 


This guide applies to both CL and S class vehicles from 2006 to mid-2009. 

S Class 221 Chassis

  • S 280 S300 
  • S350
  • S400 
  • S450
  • S500
  • S550
  • S600
  • S63 AMG

CL Class  216 Chassis

  • CL550 
  • CL600
  • CL63 AMG