auxiliary battery what is if for?

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sean1

Member
Joined
Jun 30, 2017
Messages
35
Car
E280 CDI
So my auxiliary battery failed and was driving for a week without it, and in the time it took to replace i never noticed any difference, does actually do any thing or is it just to boost the main battery?

Also after driving my partners new golf then going back to my car I noticed just how poor my head lights are do the xenon bulbs dim over the years?
 
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The AUX battery comes into circuit if the main battery voltage drops too low.

Yes, xenon bulbs do dim over time.
 
The AUX battery comes into circuit if the main battery voltage drops too low.

Yes, xenon bulbs do dim over time.

Thanks, This is the first car I've had with xenons, can xenons be replaced just like you would h7 bulbs?
 
Yes, a bit more fiddly to fit but doable. Replace as a pair.
 
Sean1, what model and year is your vehicle? The auxiliary batteries have different functions in different models.
 
The auxiliary battery powers less vital functions. In your case it's "convenience functions" like stop/start, radio, parktronic, heated seats, and the like. It's more "famous" / infamous on the R230 where it powers the roof mechanism, and can be more of an issue on convertibles which are left parked up / unused for several months at a time. (So running down the battery)

As for whether you needed to replace it, it depends on how often it has failed. If it was a one-off after not using the car for a while, you probably only needed to recharge the battery, either through a long drive or by use of a battery conditioner. it's a classic winter issue.

I appreciate that you've already replaced the battery but I'm making the point for others who will come across this thread in the future.
 
Yes MB have messed around with batteries over the years,it would be interesting if someone put together a list of models and what batteries they have,my W221 and I think the W220 have two batteries,a giant one in the boot or in my case behind the back seat reached from the boot, as I have posted before,if you look on battery web sites you get any number of big batteries for the boot,these run everything electrical on the car ,the smaller battery found in the engine compartment just starts the car,this one is never found on web sites,this state of affairs changed around 2009,where it seems one bigger battery in the engine bay was fitted, my battery is just about starting the car so it looks like I need one,I suspect mine is the original,so it has lasted well,the weird thing is that this battery is stock size in height and width,but is shorter in length than batteries found on web sites,as always it will be a race against time as from Friday my car will be parked up for a week and without a new battery it be a call out to the AA which I would like to avoid.
 
The auxiliary battery powers less vital functions. In your case it's "convenience functions" like stop/start, radio, parktronic, heated seats, and the like. It's more "famous" / infamous on the R230 where it powers the roof mechanism, and can be more of an issue on convertibles which are left parked up / unused for several months at a time. (So running down the battery)

As for whether you needed to replace it, it depends on how often it has failed. If it was a one-off after not using the car for a while, you probably only needed to recharge the battery, either through a long drive or by use of a battery conditioner. it's a classic winter issue.

I appreciate that you've already replaced the battery but I'm making the point for others who will come across this thread in the future.

Not correct, certainly not on a 2005 W211.

As posted before the AUX battery supports the main (systems) battery should charge drop critical. The main battery supplies power to ALL functions.

See this MB training doc, hopefully it will clarify how the dual battery system works on the W211

Dropbox - 319 HO Dual Battery (ACB - ICC) 11-29-02.pdf

The function of the two batteries is different from the system in the R230, where the front mounted battery only powers the starter. The boot mounted battery supplies power to all other functions. See training doc below

Dropbox - R230 Dual Battery System 11-28-02.pdf
 
Not correct, certainly not on a 2005 W211.
As posted before the AUX battery supports the main (systems) battery should charge drop critical. The main battery supplies power to ALL functions.
/QUOTE]

Apologies & thanks for the correction !
 
Remember all this lead acid battery/alternator/ starter / compressor stuff is shortly to be no more as cars move on to incorporate 48 volt multipurpose inline electrical machines in their drivelines powering electrical ancilliaries with lithium ion batteries.
Why Mercedes’ new inline six matters, even if no one is sure when we’ll see it

mgu.JPG
 
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Lexus hybrid anyone??
 
I have a November 2007 W204 C320,...It is used for relatively short journeys and consequently is no stranger to the battery charger !!
I have heard that some earlier Mercedes like mine do have an auxlilliary battery - would my model have one, and if so where would I
it be located ?

Many thanks
Markyar
 
I have a November 2007 W204 C320,...It is used for relatively short journeys and consequently is no stranger to the battery charger !!
I have heard that some earlier Mercedes like mine do have an auxlilliary battery - would my model have one, and if so where would I
it be located ?

Many thanks
Markyar
I think you will find it in the boot on the right hand side at the back, it's covered by a square plastic box.
 

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