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Secondary Backup Battery Replacement Instructions


Is your Mercedes-Benz developing electrical problems? Maybe you are getting a Visit Workshop Malfunction? Don’t panic; this can be an easy repair. You can fix this problem in less than 20 min and spend under $100. Suppose your car has been starting fine, but you keep getting the red warning on your instrument cluster that shows you a symbol of the battery. In that case, your Auxiliary/secondary 12-volt battery may need replacing. Fortunately, changing the aux/secondary battery is more manageable than changing the oil on your Mercedes-Benz.


Make: Mercedes-Benz
Model: E C CLA SLK ML S Class
Years: 2003-Present
Difficulty: Easy
Cost $45-$90
Time: 20 Minutes
Frequency: Battery lasts  4-7 years


Disconnecting the main battery before changing the auxiliary battery is recommended. The main battery is located in the trunk. Locate it and disconnect the negative terminal.

Parts & Tools Required

To complete this repair, a new auxiliary battery is required. Here are the requirements for the battery:

  • 12 Volt
  • 12Ah
  • 170 Ampere
  • Sealed
  • AGM Battery

You can go with the OEM Mercedes-Benz Auxiliary battery, or you could go with a more cost-effective alternative that meets the specifications. Here are some batteries we found on Amazon. Some were designed for motorcycles but can also be an auxiliary battery for your Mercedes-Benz. Links are provided below; if you click on any of them, you will be taken to Amazon to read reviews and check prices. Most of these batteries were listed for under $100, some as low as $45.

Replacement Aux Battery for Mercedes-Benz

Tools Required

To change the auxiliary battery, you will need a 10 mm wrench.

DIY Instructions on How to Replace Auxiliary battery


Make sure you have your emergency brakes set.

STEP 2 Open Hood

Pull on the hood release found under the dash on the driver’s side. Open the hood by pulling on the hood release located by the front grill.

STEP 3 Remove cabin air filter housing

The auxiliary battery is located under the cabin air filter housing. Locate the cabin air filter housing on the left of the engine bay. Remove the plastic bolt that holds the cabin air filter in place, then lift the cabin air filter housing to access the auxiliary battery.

STEP 4 Disconnect battery terminals

FIRST, remove the NEGATIVE battery terminal using a 10 mm socket. Then, remove the POSITIVE battery terminal.

STEP 5 Remove the battery bracket

Remove the battery bracket using a 10 mm wrench.

STEP 6 Remove the old battery

Lift the old battery out of the vehicle.

STEP 7 Install new battery

Once you place the new battery in place, fasten the bracket first. Then, connect the POSITIVE battery terminal. Connect the NEGATIVE terminal last. Place the cabin air filter housing back over the auxiliary battery.

Recommended Parts

VIDEO Related How To Repair Videos

YouTube video


YouTube video

Related Articles

Here is a list of related how-to articles.

Frequently Asked Questions

How many batteries does my Mercedes-Benz have?

Many Mercedes-Benz cars starting from 2003 have two batteries. The main battery is typically in the trunk, and the auxiliary is in the engine bay. Not all models have two batteries, though.

What is the reason for having two batteries on my Mercedes-Benz?

The main battery, typically found in the trunk, is a full-size battery that supplies electricity to the onboard electrical system under regular operation. The additional battery, often called the auxiliary or secondary, is a smaller battery used as a backup power supply in case the main battery fails.

What is the function of the auxiliary battery?

The additional battery is a backup power supply if the main battery fails. You can learn more about the secondary battery here.

2012 – 2014  C250
2008 -2014 C300
2008 – 2014  C350
2008 – 2013 C63 AMG
2014 – 2014 CLA250
2014 – 2014 CLA45 AMG
2006 – 2006 CLS500
2006 – 2006 CLS55 AMG
2007 – 2010 CLS550
2012 – 2013 CLS550
2007 – 2013 CLS63 AMG
2004 – 2009 E320
2003 – 2003 E320 Base Sedan
2006 – 2013 E350
2003 – 2006 E500
2003 – 2006 E55 AMG
2007 – 2011 E550
2012 – 2013 E550 Base
2007 – 2011 E63 AMG
2013 – 2014 GLK250
2010 – 2014 GLK350
2013 – 2013 SL550
2013 – 2013 SL63
2012 – 2013 SLK250
2012 – 2013 SLK350
2012 – 2013 SLK55 AMG

Can I drive my car with a failed auxiliary battery?

Even if the auxiliary battery may have failed, you may notice that your car starts and runs fine. You can typically drive the car if you are stuck away from home. We don’t advise that you continue to drive the vehicle with a failed auxiliary battery. It is a concern if the main battery dies. Several Mercedes-Benz models use SBC (Sensotronic Braking System) brakes or brakes by wire. In that case, you may experience reduced braking power or no brakes.

Why does the red battery light display on the dash when I start the car?

TBenz_auxiliary_secondary_battery_replacement_How_to_DIY_05hat’s because the car has detected that the trunk’s auxiliary or primary battery has low voltage. You could have a system that drains your battery when the vehicle is parked, or one of the batteries is failing. If the car starts fine, there is no hesitation in starting; we would recommend replacing the auxiliary battery. If you still have the red light, the primary battery may be the problem, or the electricity drained overnight.

Applicable Part Number

Mercedes-Benz Secondary Backup Auxiliary Battery

  • Genuine Original 2115410001
  • Manufacturer Part Number:  2115410001
  • Interchange Part Number: A 2115410001
  • MB211-541-00-01

GENUINE MERCEDES Auxiliary Battery Relay


  1. This is NOT instructions for the CLA250 Aux Battery. 1) the battery is in the engine compartment, not the trunk as stated and 2) the cabin air filter is NOT on the left side of the engine compartment. I’ve yet to find where my aux battery so I can replace it.

  2. I had the Battery Malfunction problem on my Mercedes-Benz and replaced the auxiliary battery following this guide.

    Error message gone. Thank you!

    • Hi fanatic. Just bought 2013 MB from auctions. Message on dashboard says Auxilliary battery malfunction’ Is this the same message you had. Also how much was the new battery?
      Thank you

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