Mercedes-Benz E-Class W211 Auxiliary Battery Replacement

Symptoms

• Auxiliary battery malfunction on the dashboard
• Battery protection: Convenience functions temporarily unavailable

What you will need

• W211 Auxilary Battery 
• 10mm deep socket
• Ratchet wrench
• Battery Terminal Protector

Procedure

1. Open the hood and locate the auxiliary battery on the passenger side of the engine bay. 
2. Remove the 10mm plastic nut from the cabin filter housing. 
3. Remove the 10 mm nut from the top bracket. Lift the bracket. 
4. Remove the 10mm bolt from the negative battery terminal. 
5. Remove the 10mm bolt from the positive battery terminal. Be extremely careful so that the positive cable does not come in contact with any metal parts.  
6. Remove the old battery and place the new battery in place. Connect the positive cable first. Connect the negative cable last. Spray battery terminal protector on the battery post to prevent corrosion. Install the cabin filter lid. 

No programming or coding is required. Once you replace the auxiliary battery on your W211 E-Class, the warning message should disappear from the dashboard.