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Auxiliary battery location W221

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Auxiliary battery location W221

 
Old 03-29-2016, 02:01 PM
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Auxiliary battery location W221

Hi,
I have a message "Auxiliary battery malfunction". I have bought a new one (part number N000000004039), but I don't know where to find it in the car?
When I asked a parts man at the dealer, he told me that the location in behind the instrument cluster.
Can anyone confirm that? It seems to be a very strange place to put battery there.

Thanks a lot!
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Old 03-29-2016, 02:10 PM
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Deep in the trunk. Behind where your back rates on the back seats. On the bottom right hand side.


Your parts guy knows where it is on a civic, not a Mercedes Sclass.

Last edited by mercedesbenzs55; 03-29-2016 at 02:12 PM.
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Old 03-29-2016, 02:12 PM
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Thank you!
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Old 03-29-2016, 02:13 PM
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what year is your car? Facelift cars AUX batteries are in the dash, under the steering wheel.
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Old 03-29-2016, 02:19 PM
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2010
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Old 03-29-2016, 02:20 PM
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Originally Posted by xpl0sive View Post
what year is your car? Facelift cars AUX batteries are in the dash, under the steering wheel.
Thank you! Any idea how to get there?
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Old 03-29-2016, 03:28 PM
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From another forum...

Open driver door and unmount lateral pannel of dashboard (1 in picture)
Unmount the down side of dashboard (you have 3 screw above pedals )(2 in picture)
when you look from pedals in up you will see on lateral pannel (sign with 3 in picture) a metalic box
fixed with a screw from outside who keep auxiliary battery.
Good luck

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Old 03-29-2016, 03:30 PM
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Originally Posted by mercedesbenzs55 View Post
Deep in the trunk. Behind where your back rates on the back seats. On the bottom right hand side.


Your parts guy knows where it is on a civic, not a Mercedes Sclass.
or the parts guy knows exactly what he's talking about
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Old 03-29-2016, 09:24 PM
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Originally Posted by xpl0sive View Post
or the parts guy knows exactly what he's talking about
Perhaps he should start banging the panels with a rubber mallet until he finds it.
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Old 03-29-2016, 10:03 PM
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Originally Posted by DaveW68 View Post
Perhaps he should start banging the panels with a rubber mallet until he finds it.
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Old 01-25-2017, 05:47 AM
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Does any one know where the Aux battery is on a pre facelift 2007?
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Old 01-25-2017, 10:40 AM
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Originally Posted by dannyjna View Post
Does any one know where the Aux battery is on a pre facelift 2007?
Behind the passenger side rear seat back. Access through the trunk by taking out the spare tire cover and screws that hold the net tie downs. After that's out, you will be able to pull the seat back panel down and take it out to expose the battery. That panel does not come out easily. You need an AGM H8 battery, which you can find at Walmart or any auto parts store. Usually around $130-160 for the battery which is much cheaper than the Mercedes branded one (which is identical to the H8).

FWIW, you do not need to put a battery tender on the car while changing it. Your presets and everything else will run off your starter battery while you're changing out the aux batter.

Last edited by DaveW68; 01-25-2017 at 10:42 AM.
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Old 01-25-2017, 11:04 AM
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thanks!

This is for 2007 w221 yes?

Its a small motorcycle looking battery?

I keep getting shifting errors but any faults are under voltage
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Old 01-25-2017, 12:14 PM
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Originally Posted by dannyjna View Post
thanks!

This is for 2007 w221 yes?

Its a small motorcycle looking battery?

I keep getting shifting errors but any faults are under voltage
Yes, 2007. It is a full size battery in the trunk. You'll see when you get the H8 battery. The starter battery under the hood is the smaller battery.
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Old 02-08-2019, 08:11 AM
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2012 S550 battery tender

Hi everyone, read several posts on battery tenders for my 2012 S550. Its still not clear to me regarding the auxiliary battery location. Just got the car and have not checked, but I believe the auxiliary battery is trunk mounted right side behind passenger seat under floor. Can anyone confirm this? Also, the car will be stored about two months, should I place trickle charger on both the cranking battery and the auxiliary battery?
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Old 02-08-2019, 09:53 AM
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Originally Posted by Brady9229 View Post
Hi everyone, read several posts on battery tenders for my 2012 S550. Its still not clear to me regarding the auxiliary battery location. Just got the car and have not checked, but I believe the auxiliary battery is trunk mounted right side behind passenger seat under floor. Can anyone confirm this? Also, the car will be stored about two months, should I place trickle charger on both the cranking battery and the auxiliary battery?
In the 2010+ models, the aux battery is a small battery under the dash on the driver's side. Kind of a PITA to change out from what' I've heard....and no options to buy it at an auto parts store. I think it is more of a backup to the main battery under the hood....which controls all of the accessories along with the starting capability. If you are going to put a tender on your battery, you only need to worry about the one under the hood.
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Old 02-08-2019, 02:41 PM
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Thanks for your input. To be clear, there is not another battery in the trunk compartment on a 2012 S550?
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Old 02-08-2019, 02:59 PM
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Originally Posted by Brady9229 View Post
Thanks for your input. To be clear, there is not another battery in the trunk compartment on a 2012 S550?
That is correct. Only the 2007 to 2009 models of the W221 had the auxiliary battery in the trunk area. Those models also had a smaller starter battery under the hood. Your car has the full size AGM H8 sized battery under the hood which operates starting and all other components.
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Old 02-08-2019, 03:02 PM
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Thumbs up Battery location

Thanks again, got it
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Old 02-09-2019, 12:35 PM
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Originally Posted by DaveW68 View Post
In the 2010+ models, the aux battery is a small battery under the dash on the driver's side. Kind of a PITA to change out from what' I've heard....and no options to buy it at an auto parts store. I think it is more of a backup to the main battery under the hood....which controls all of the accessories along with the starting capability. If you are going to put a tender on your battery, you only need to worry about the one under the hood.
Mostly itís to operate the solenoids that move transmission into gear. Kind of a bummer otherwise to have a dead battery and canít get car out of gear to tow it.
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