C204 Auxiliary Battery

Bennn

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Hi Guys

Not long owned my C220 CDI and working through a few minor issues with it (love the car generally though)

The Eco stop start system doesn't seem to be working on it. I know that it needs a lot of parameters to work; however I've taken it on a 2 hour journey today and it still wasn't ready so I suspect there may be something wrong.

Google seems to suggest auxiliary battery is likely at fault. I know this is in the boot and have a mulitmeter so can check the voltage.

Does anyone know what it should be putting out?

If it is faulty, is it a dealer only part and I'm assuming they are easy to fit?

Cheers

Ben
 

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Bennn

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Fully charged, the auxillary battery should be showing around 12.7v.
I'd get a price from MB Grangemouth, who discount goods for MB Club members and deliver next day for around £5
Next take a look at the motorcycle batteries at Tayna and see what a Varta or Yuasa equivalent would cost.

Varta Motorcycle Batteries - Motorcycle Batteries
Yuasa Motorcycle Batteries - Motorcycle Batteries

Easy to fit once the holding bracket is removed. Neg terminal off first and replaced last.

Brilliant thank you.

Do you know if I am safe to disconnect this with the main battery still connected. If possible I don't want all the settings on the car getting reset.

Cheers

Ben
 

AMGeed

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Its fine to disconnect with the main battery in place Ben.

Any lost settings (windows and sunroof) are sometimes lost when disconnecting the main battery.
 
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Bennn

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Its fine to disconnect with the main battery in place Ben.

Any lost settings (windows and sunroof) are sometimes lost when disconnecting the main battery.

Thanks that's brill I'll check the voltage and if its low sort a replacement.
 
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Bennn

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Its fine to disconnect with the main battery in place Ben.

Any lost settings (windows and sunroof) are sometimes lost when disconnecting the main battery.

Got the battery out now and checked the voltage which is showing 13.12V

It's the original by the looks of it.

The stop start has worked once the morning, oddly right at the start of a journey and then after that the eco went yellow and it hasnt worked since.

I'm a little stumped now. Any ideas what to check next? Main battery?

Cheers

Ben
 
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Bennn

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Main battery is only showing 12.25V though. Could this be the culprit.

Does anyone know if you can charge these sorts of battery?

I've a knock off ctek charger I bought from Lidl a few years ago.
 

ToeKnee

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Just because the voltage is good doesn't necessarily mean the battery is good. The aux battery on mine was showing good voltage and the stop start worked if everything else was switched off, if the lights came on or I turned the a/c on then S/S stopped too because the battery didn't have enough oomph to power it all. New battery and everything sorted, I can have all accessories on and stop start works seamlessly.
 
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Bennn

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Just because the voltage is good doesn't necessarily mean the battery is good. The aux battery on mine was showing good voltage and the stop start worked if everything else was switched off, if the lights came on or I turned the a/c on then S/S stopped too because the battery didn't have enough oomph to power it all. New battery and everything sorted, I can have all accessories on and stop start works seamlessly.

Interesting. Well the main battery was a bit low on voltage so is being charged now so I may as well see if that gets it working properly. If not I guess I will need to look at the aux battery again!

I did find it odd that it worked again very briefly today. Only reason I can think why is I think the previous owner did little journeys in it (as the average mpg over the last 10k was only 40). I take it on much longer runs so maybe I've put enough back into it to get it working again (although not for long)

So optimistically I'm hoping a good charge will sort it out.

Does that seem logical?
 

OneForTheRoad

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Maybe stored amps are more important. A 12v battery will almost always be 12v but the amps drop due to starting ,lights,etc etc.
 
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Bennn

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Maybe stored amps are more important. A 12v battery will almost always be 12v but the amps drop due to starting ,lights,etc etc.

Yes they are 12v but as far as I know when it gets down to 12v they are usually dead. 12.7v Is the normal figure anything below this means it needs charging, hence why mine is hooked up now.
 

OneForTheRoad

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Yes they are 12v but as far as I know when it gets down to 12v they are usually dead. 12.7v Is the normal figure anything below this means it needs charging, hence why mine is hooked up now.


Oh right. Sorry.
 

MrGreedy

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I'd suggest any battery that is straying into the 7 to 9+ year category should be changed as a matter of course. Unless you think you can get away with it for a few months and you are planning to move the car on in that time. Buyer beware and all that.
 

wongl

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I'd suggest any battery that is straying into the 7 to 9+ year category should be changed as a matter of course. Unless you think you can get away with it for a few months and you are planning to move the car on in that time. Buyer beware and all that.
This is good advice from MrGreedy. Unless you regularly charge your batteries overnight, pushing past 10 years for a battery on a modern car with stop/start will be difficult/extremely lucky!
 

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