Changing the main battery Class C

[sceh]

Sorry if this is repeated but I can't find the answer in the forum.
I need to change the battery in my 2011 Class C diesel since it has done ten years..though only 50K miles.
Is the main battery responsible for the start/stop functionality or is it the auxiliary one in the boot? I ask this because I don't use the start/stop and batteries saying they are 'start/stop' are twice the price.
As an aside, my start/stop hasn't worked for years which might explain why I never use it! Could it be that this doesn't work because the MAIN battery is a bit weak?
thanks and sorry if this has been asked and answered a million times

 

[geoffus]

You need both batteries in good condition to have start/stop feature to work correctly.
I have bought 2 batteries from Tanya recently and didn’t think they were too expensive and are stop/start compatible

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www.tayna.co.uk

 

[sceh]

Thanks.
I heard that if the aux battery is bad then things could go wrong when I remove the main battery but am not sure if this is true. If I change the aux battery, are there any issues (other than finding where to buy one..)?

 

[geoffus]

No issues at all, you may need to reset the windows and mirrors after replacing the starter battery but that’s it.
The aux batteries are relatively cheap fix for stop start, but a few people on here don’t bother as it’s a pain, I never use mine.

 

[keith of kent]

Another + for Tayna. I got Varta the same as factory fitted one for a very good price, and delivered the next day

 

[Petrol Pete]

+1 for Tayna , I have used them many times. BUT , make sure you get the correct battery when ordering because the cost of sending it back is on you.

And it's very expensive to do so.

 

[JHS]

Thread hi-jack!
Where is this Auxiliary battery in a s205 250d?

 

[markjay]

Another + for Tayna. I got Varta the same as factory fitted one for a very good price, and delivered the next day

It depends on what you mean by 'the same'. The factory-fitted batteries are made by Varta exclusively for MB, and are not available for purchase directly from Varta. However, you can obviously buy other models of Varta-made batteries that will fit your Mercedes Benz.

 

[markjay]

Thread hi-jack!
Where is this Auxiliary battery in a s205 250d?

Typically on the W205 it's a capacitor (not an actual bulky lead acid battery) under the carpet in the passenger footwell.

Also, you'll get an error message on the dash if it's faulty.

 

[sceh]

Curiously there is no mention of the auxiliary battery in the owners handbook and the WIS/ASRA from Mercedes tells you how to remove it but gives no specification details such as aH or physical size. Does this mean that changing it is such a rare and needless exercise that it need not be mentioned? Odd.
Anyone know?

 

[sceh]

Here is a good video showing how to change the auxiliary in any Mercedes where it is installed in the boot. Simple

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[sceh]

Changed both batteries and the start/stop works again!
The only glitch was the breather tube for the auxiliary is bigger than the hole in the battery (Exide) so I shaved it and glued it but I guess that even if it is missing it makes little difference in practice (?)