2008 W221 S320 CDI - Proper way to change rear (consumer) battery and should it be a AGM or Non-AGM?

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mbenz1

MB Enthusiast
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Jul 27, 2010
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1,009
Car
'08 C320 CDI Sport w/ Advcd. Agility Package
Hi All,

Hope you are well.

My dad's 2008 S320 CDI (has no stop/start feature) is showing 11.8V with the car off which indicates a low battery. The car's engine fan is also coming on randomly on cold start-up and a Yellow coolant light displays in the dash.

Before we chase the engine fan problem, we'd prefer to change the rear battery as 11.8V is low indeed and the car still has the original MB battery in the rear (we think it could be the low battery causing the engine fan issue)

I want to know if I can simply disconnect the - cable then disconnect the + cable and remove the battery or should I first disconnect the starter battery (in the engine bay) and then disconnect the rear battery? Can I get away without providing aux power to the car whilst the battery is disconnected?

Also, I have checked various sites and they all are saying that the car requires a AGM battery at the rear - can anyone confirm if the original MB battery at the rear is supposed to be AGM or non-AGM? I rang Mercedes but they did not have that information on hand, as usual.

Finally, if the battery is supposed to be AGM, then I take it that no coding is needed to tell the car that a new battery has been fitted to it?

Thanks.
 
Obvious question - if it’s the original battery, what’s fitted currently? (no pun intended) ;)
 
Obvious question - if it’s the original battery, what’s fitted currently? (no pun intended) ;)

That's the problem - the battery is surrounded by various modules and units and due to this the label on the battery can't be read so I can't even see what the Ah rating is either. All I know is that it is a 12V battery...

Plus from what I know, many manufacturers like MB and BMW don't even mention AGM on their batteries. My 2008 BMW 3 Series needed a new battery and it turned out it needed a AGM battery despite it having no stop/start and no information on the original battery label to indicate it was a AGM battery.
 
Stop start and 320 cdi needs a AGM battery
 
Stop start and 320 cdi needs a AGM battery
Thanks for clarifying. So all 320CDIs need AGM batteries (consumer AGM battery in the case of a W221) regardless of whether they have stop-start or not (mind you I don't think there is a Merc 320 CDI which was offered with stop-start??)
 
Have you tried charging it ? lots of batteries are showing low at the moment because lack of use and cold weather.


Enter your reg here to find the battery,

 
Cannot confirm that ALL 320 Cdi's need an AGM battery , but I had a 2008 E320cdi without stop/start and it needed an AGM
 
Ok thanks for clarifying.

Can anyone confirm on the correct way to remove the rear consumer battery in the W221 S-Class pre-facelift model? Is it simply just a cause of disconnecting the wires, and replacing the battery? Bear in mind this model has a another 12V starter battery in the engine bay which is connected to the rear battery via the Power Module....
 
@mbenz1, I can understand wanting to try to do this yourself but when I looked at what was involved in replacing the CL consumer battery I took it to the MB dealership and let them do it. Not only does it look (very) complicated but you need to be a contortionist with very strong arms.

My consumer battery had run low and threw up a load of fault codes which they cleared at the same time. I thought the cost reasonable considering what was involved so maybe worth getting a quote? At least you know you'll get the correct battery.
 
Cannot confirm that ALL 320 Cdi's need an AGM battery , but I had a 2008 E320cdi without stop/start and it needed an AGM

@mbenz1, I can understand wanting to try to do this yourself but when I looked at what was involved in replacing the CL consumer battery I took it to the MB dealership and let them do it. Not only does it look (very) complicated but you need to be a contortionist with very strong arms.

My consumer battery had run low and threw up a load of fault codes which they cleared at the same time. I thought the cost reasonable considering what was involved so maybe worth getting a quote? At least you know you'll get the correct battery.
Its actually a very simple job to remove the battery! Remove the carpeted trim panel by hand, which will reveal all modules behind the rear seats, then simply remove the 10mm bolt and clamp and pull the battery out! I've done some other electrical work on the power module which sits right on top of the battery and yes it is hard to get access down there, but I managed to 'lie down' in the boot and do the work!
Is this your battery ?
Nope, its a standard size battery (like the starter battery) - its a proper battery. But thanks for looking this up anyway
 
Managed to have a little peep today and I did notice it says VRLA! So its not an AGM battery unfortunately.

I will some other day 'lie in the boot' and see if I can get the part number and even better, the Ah rating and CCA rating. I think I will be able to get the part number and hopefully I can find that on eBay and get the details from there!
 
Managed to have a little peep today and I did notice it says VRLA! So its not an AGM battery unfortunately.

Careful, no reason it cannot be a VRLA AGM.

I will some other day 'lie in the boot' and see if I can get the part number and even better, the Ah rating and CCA rating. I think I will be able to get the part number and hopefully I can find that on eBay and get the details from there!

Why not just ask one of the many MB good parts sellers, ebay etc. for a price or ask here via VIN or reg. ?
Would remove all the guess work. ;)
 
Careful, no reason it cannot be a VRLA AGM.



Why not just ask one of the many MB good parts sellers, ebay etc. for a price or ask here via VIN or reg. ?
Would remove all the guess work. ;)
Ah! Of course, AGM VRLA is also possible! Will keep this in mind.

I will dig out the VIN and post it here soon
 
Careful, no reason it cannot be a VRLA AGM.



Why not just ask one of the many MB good parts sellers, ebay etc. for a price or ask here via VIN or reg. ?
Would remove all the guess work. ;)
Here is the VIN for my dad's S320 CDI: WDD2210222A190558. If anyone could use this to hopefully let me know the part number for the battery in the car, that would be great.

I have got a trickle charger, so my plan is to charge the battery to 100% and then see how the car behaves. Thanks.
 
Here is the VIN for my dad's S320 CDI: WDD2210222A190558. If anyone could use this to hopefully let me know the part number for the battery in the car, that would be great.

I have got a trickle charger, so my plan is to charge the battery to 100% and then see how the car behaves. Thanks.

Main Battery: A0055411301
Backup Battery: N000000004039
 
Nothing wrong in charging the big battery behind the rear seats in your car,it is quiet easy to change as well as it slides out and of course the new one will slide in.
 
Note that you can charge the rear battery from a connector pole at the engine bay, under a small plastic cover.
 
Main Battery: A0055411301
Backup Battery: N000000004039
Thanks a lot for this. I did a Google search and found one on eBay and can now see what ratings it has: 60Ah and 680A! Thanks a lot. Just got to find out if its a VRLA AGM or just a VRLA... will look into this further.
Nothing wrong in charging the big battery behind the rear seats in your car,it is quiet easy to change as well as it slides out and of course the new one will slide in.
Yes, it is easy indeed.
Note that you can charge the rear battery from a connector pole at the engine bay, under a small plastic cover.
I didn't know about this? Would this method be okay when using a standard trickle charger purchased off Amazon? Also, will both batteries be charged via this method (not that there is no harm in charging the other battery :)?
 
I didn't know about this? Would this method be okay when using a standard trickle charger purchased off Amazon? Also, will both batteries be charged via this method (not that there is no harm in charging the other battery :)?

The starter battery is not connected with the consumer battery (when the car is parked), both batteries need to be charged separately (if both need a charge). I cannot remember if the W221 has a jump start pole at the engine bay, the starter battery poles are anyway ease to reach.

Cannot really comment on your trickle charger, must be fine if it is built for your battery type (AGM).
 

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