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Pelican Technical Article:

Auxiliary Battery Replacement

Nick Czerula

Time:

1.5 hours

Tab:

$50

Talent:

***

Tools:

Set of sockets 10mm, flathead screwdriver

Applicable Models:

Mercedes-Benz W211 (2003-09)

Parts Required:

Auxiliary battery

Hot Tip:

Wear eye and hand protection

Performance Gain:

Renew worn out battery

Complementary Modification:

Replace main battery

Mercedes-Benz W211 Models are equipped with two batteries. The batteries in your w211 are an absorbed glass mat (AGM) type, which is different from the older style lead acid batteries. AGM batteries house the battery acid in glass mats. Lead acid batteries house the fluid between lead plates. AGM batteries are made of very thin glass fibers woven into a mat. This increases the surface area enough to hold sufficient electrolytes on the cells for their lifetime. Lead tends to absorb some of the acid, shortening battery life. There are positives and negatives when using AGM over lead acid batteries. For example, an AGM may charge faster, but is more susceptible to damage from overcharging. They produce less gas than a lead acid battery, can be mounted in any position (do not leak) and are safer for the environment because of this. One downside is the increased cost. Also, charging systems have evolved along with the battery type, allowing greater control of charging current via sensors and computer controlled adaptation.

The main battery in W211 models is located in the center of the trunk, mounted in a well, below the trunk carpet. The auxiliary battery is located in the right side of the engine compartment, near the HVAC intake. When replacing your battery, be sure to use a high quality unit. Replacing the battery can be done in a short amount of time. Read the battery connection notes before disconnecting the battery. Before disconnecting your battery, remove the key from the vehicle and store it in a safe place and note the radio presets. When the battery is reconnected or loses its charge, the following items may need attention (depending on vehicle equipment). You may have to reset your clock, enter the radio presets, initialize power windows, initialize the sunroof and normalize the steering angle sensor. See our tech article on battery replacing, for info on the main battery and jump-starting.

The auxiliary battery supplies power for a limited time if system charging or battery voltage drops. The battery control module monitors system voltage. If voltage reaches a low point, the auxiliary battery relay closes to connect the battery to the vehicle fuse blocks.

Remember that your car may have been serviced before and had parts replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have so be prepared with different size sockets and wrenches.

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If you're working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Never work on your vehicle if you feel the task is beyond your ability.

Our vehicle may vary slightly from yours as models do change and evolve, as they grow older. If something seems different, let us know and share your info to help other users. Do you have questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

The auxiliary battery is located in the right side of the engine compartment, near the HVAC intake.
Figure 1

The auxiliary battery is located in the right side of the engine compartment, near the HVAC intake. To replace it, begin by removing the 10mm plastic nut from the cabin microfilter lid (green arrow).

Lift and remove the cabin microfilter lid from the HVAC intake.
Figure 2

Lift and remove the cabin microfilter lid from the HVAC intake.

Remove both terminal plastic covers (green arrows).
Figure 3

Remove both terminal plastic covers (green arrows). They will unclip and remain attached to the cables via plastic tethers.

Using a ratchet and a 10mm socket, disconnect the negative (-) battery cable (green arrow).
Figure 4

Using a ratchet and a 10mm socket, disconnect the negative (-) battery cable (green arrow). Move the negative (-) cable aside and cover so it does not accidentally come in contact with the battery terminal.

Release the locking clip and open the battery safety terminal cover.
Figure 5

Release the locking clip and open the battery safety terminal cover. This photo shows the lid open. Then using a ratchet and a 10mm socket, loosen the positive (+) battery cable (green arrows). Lift the positive (+) battery cable off the battery and lay it aside. Cover the cable end so it does not accidentally come in contact with the battery terminal.

Using a 10mm socket, remove the battery hold down (red arrow) nut.
Figure 6

Using a 10mm socket, remove the battery hold down (red arrow) nut. Then, flip the hold down up toward the firewall (inset).

Lift the battery up and remove it from the well.
Figure 7

Lift the battery up and remove it from the well. Be careful and make sure you have a good grip. The battery can be slick. You will have to move cables around and keep them out of the way as you remove the battery from the vehicle. Clean the battery compartment thoroughly. Clean the corrosion from the battery cable ends if present. Inspect the battery part # and replace it with a new battery. Here are the specs for the battery: Auxiliary Battery: AGM, 12V, 12Ah, 170 A (DIN).

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Comments and Suggestions:
Captain Comments: What is the transmission ECM fault codes and how can i rectify it
Thanks alot for other problem reported to you,they have been completely solved.
November 27, 2016
  Followup from the Pelican Staff: That is codes in the transmission control module. Repair the part of system the fault codes are reporting are at fault. - Nick at Pelican Parts  
wayner Comments: Where can I find the auxziliary battery on a 2009 s550 mercedes ?
November 14, 2016
  Followup from the Pelican Staff: I believe it is behind the instrument panel behind the fuse panel. - Nick at Pelican Parts  
Mig373 Comments: Hi.Ive got 2005 Mercedes E280 W211 3 Cdi.Everytime I turn warm engine it turns very lazy but colt starts with no problem.I checked the battery and it's 12V 70Ah 760Aen.My question is any chance that this battery its to weak and I need 100Ah one?If I fit 100Ah one is there any risk?Regard
November 14, 2016
  Followup from the Pelican Staff: That may be the battery for your vehicle. To be sure, Give our parts specialists a call at 1-310-626-8765
- Nick at Pelican Parts
 
Beneto Comments: My car, 2005 e200, has been at the spraying shop for sometime now, i just went there for it and to my dismay the power windows are not responding, no air and all the lighting systems are messing up. What could be the possible cause..? Let me quickly add that it's been displaying 'visit workshop' with a battery sign for some time now even though i have changed the main battery.
October 16, 2016
  Followup from the Pelican Staff: If the battery is OK, confirm there is not voltage drop from the battery terminals to the cables and fuse panels. - Nick at Pelican Parts  
Captain Comments: I have worked on the alternator and my Mercedes e350 2006 still showing visit workshop with battery logo what is the next action.
September 16, 2016
  Followup from the Pelican Staff: What is charging voltage and current? - Nick at Pelican Parts  
Captain Comments: When am driving my Mercedes E350,between gear 1-2 the engine vibrate or if I press turtle while on sport, what could be the cause.
September 16, 2016
  Followup from the Pelican Staff: First check the transmission fluid level to be sure it is correct. Then check the transmission ECM for fault codes. If the system is not working properly, a fault code will be set. This will be your best bet when diagnosing.
- Nick at Pelican Parts
 
Vincent Comments: I have a ml 350 want components does the auxiliary battery control in my truck to no I need to replace that battery

September 14, 2016
  Followup from the Pelican Staff: The auxiliary battery supplies power for a limited time if system charging or battery voltage drops. The battery control module monitors system voltage. If voltage reaches a low point, the auxiliary battery relay closes to connect the battery to the vehicle fuse blocks. - Nick at Pelican Parts  
Captain Comments: My Mercedes e350 2006 is showing visit workshop with battery logowhat could be the cause
September 7, 2016
  Followup from the Pelican Staff: A faulty alternator or battery. - Nick at Pelican Parts  
cowboysfanokc Comments: I replaced my aux battery with a APTX14 and after replacing it with this cheaper one,now my air ride is not going up. Could this be something due to the battery. it is a AP series 12 volt agm battery
August 24, 2016
  Followup from the Pelican Staff: Doubtful. I would check the vehicle for fault codes. it may be a coincidence. - Nick at Pelican Parts  
alij Comments: can i recharge this aux battery instade of replacing it with the new one cause its expensive
August 19, 2016
  Followup from the Pelican Staff: if it is faulty, it won;t take a charge. So you'll likely have to replace it.

Give The Pelican Parts parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
 
Ivan Comments: Do i need to disconnect the main battery when i replace this one?!?
July 26, 2016
  Followup from the Pelican Staff: It is s a good idea, you can do it without as shown if you work carefully. - Nick at Pelican Parts  
Rakesh Comments: S320.where is the auxilary battery placed.?
July 25, 2016
  Followup from the Pelican Staff: what year? - Nick at Pelican Parts  
Ahmed Comments: I have mercedes e280 2008 avantgarde and i cant find any battery under the cabin filter are some models come without aux battery ?
July 17, 2016
  Followup from the Pelican Staff: We don't have that model in the US, so I can't be sure. - Nick at Pelican Parts  
Deber Comments: 2003 E320 what is in ohm sometimes I hear weird noises I just I just replaced the auxiliary battery.. Now sometimes I don't have any gauges or any windows or any air that works help what to do
July 14, 2016
  Followup from the Pelican Staff: You may have blown a fuse during battery replacement. I would start by checking the vehicle for fault codes. If multiple systems are not working properly, fault codes will be set. This will be your best bet when diagnosing.
- Nick at Pelican Parts
 
Delian Comments: Hi there, if instead of a 12 V 12 AH i put a 12V 14 Ah auxiliary battery for a mercedes e220, w211 what it will happen ?
June 14, 2016
  Followup from the Pelican Staff: Nothing, it should be fine. - Nick at Pelican Parts  
arif Comments: ok sir, i appreciate your time, However i read some where if i get a harley davidson or honda battery wit 12v 12 ah specs top mounted screw type then it would work. Please advise if you think its possible
March 2, 2016
  Followup from the Pelican Staff: Like I said, I have no experience with this and can't comment or supply a part number. Check your source for more information. - Nick at Pelican Parts  
arif Comments: Hello Nick

i dont not leave in the usa so cannot order from you because of shipping cost.

Please give me a equivalent part battery for a honda or yamaha motor bike, I am in africa and as you can imagine things are difficult to find over here
March 2, 2016
  Followup from the Pelican Staff: I don't have a part number. You can't use a motorcycle battery. - Nick at Pelican Parts  
Arif Comments: Can i replace the secondary battery with a motor bike battery ? The original battery is very expensive.
February 29, 2016
  Followup from the Pelican Staff: No. Give our parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
 
joe Comments:  I need to change the auxiliary battery on my car and I wanted to know if I need to reprogram anything once I install the new battery A 2004 e320 4matic
February 3, 2016
  Followup from the Pelican Staff: No, just replace the battery. - Nick at Pelican Parts  
joe Comments: I need to change the auxiliary battery on my car and I wanted to know if I need to reprogram anything once I install the new battery Honda A 2004 e320 4matic
February 3, 2016
  Followup from the Pelican Staff: No, just replace the battery. - Nick at Pelican Parts  
SARUP Comments: MERCEDES 2005 E320 GAS 4MATIC.WHEN TO CHANGE THE AXILARY BATTERY?
February 3, 2016
  Followup from the Pelican Staff: Test it, when it doesn't hold a charge or capacity drops, replace it. - Nick at Pelican Parts  
Majid Comments: I wanted to knw whats d ampier for auxiliary battery
January 31, 2016
  Followup from the Pelican Staff: Here are the specs for the battery: Auxiliary Battery: AGM, 12V, 12Ah, 170 A (DIN). - Nick at Pelican Parts  
Marc Comments: I have these steps done. After replaced the auxiliary battery I start driving after about 1 mile the car is cut off and stop. A new message tells me the Tele Aid is not activated. I don'ta know what to do.
August 17, 2015
  Followup from the Pelican Staff: Tele aid malfunction could be a bad connection at the module or wiring. Likely unrelated to the stall. When your engine doesn’t start you’ll want to check the basics. Check spark, fuel injector pulse and fuel pressure, volume, quality and engine compression. Are there any fault codes? Once you figure out what is missing, it will be easier to diagnose. - Nick at Pelican Parts  

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Page last updated: Sat 12/3/2016 02:45:26 AM