W211 Aux Battery

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clk320x

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I’m 99% sure I need a new one as when car is sat for a few days I get battery visit workshop and convenience features disabled.

Car starts fine so I assume main battery is fine.

Can anyone advise on the size/type/cost of the AUX battery please?

Regards,
Abs
 
It is usually more likely to be the main battery that is dropping as the Aux. one is for the SBC.

Aux. one is A2115410001, last one I bought £54 from Edinburgh in 2016.
 
I’m 99% sure I need a new one as when car is sat for a few days I get battery visit workshop and convenience features disabled.

Car starts fine so I assume main battery is fine.

I wouldn't be 99% sure,

The message will appear if the main battery performance drops off. And the car may well still start with no apparent problems.
 
It is usually more likely to be the main battery that is dropping as the Aux. one is for the SBC.

Aux. one is A2115410001, last one I bought £54 from Edinburgh in 2016.
Thanks Pat but I get the convenience features disabled I thought this meant the Aux?

TBH - I left the car sitting for a month and it still started hence I assumed main battery was ok as I’d expect some difficulty starting otherwise?
 
I wouldn't be 99% sure,

The message will appear if the main battery performance drops off. And the car may well still start with no apparent problems.
Hmm true. I think the main battery was replaced by the p/o however and the aux may well be original
 
TBH - I left the car sitting for a month and it still started hence I assumed main battery was ok as I’d expect some difficulty starting otherwise?

Car may start fine even though the message appears.

Modern batteries are resilient - modern cars are picky about how they perform. You could have a degraded battery that will still start the car with no problems but a voltage drop that causes the message. I've seen something similar with our BMW where the car would start fine but there were intermittent warnings of other problems - it took a while to get to the bottom of it.

If the car has been left for a while has it been charged properly since? Decent long run or via a charger? And does the message warning about convenience functions still appear?
 
Car may start fine even though the message appears.

Modern batteries are resilient - modern cars are picky about how they perform. You could have a degraded battery that will still start the car with no problems but a voltage drop that causes the message. I've seen something similar with our BMW where the car would start fine but there were intermittent warnings of other problems.

If the car has been left for a while has it been charged properly since? Decent long run or via a charger? And does the message warning about convenience functions still appear?
When left for 1-2 days it’s fine, if you leave it sitting for a week or so it’ll start but come up with the error on the first start, ‘battery visit workshop’ and ‘convenience features’... then when you restart the car after a 10 min drive all errors clear!
 
It is usually more likely to be the main battery that is dropping as the Aux. one is for the SBC.

Aux. one is A2115410001, last one I bought £54 from Edinburgh in 2016.
Thanks Pat,

Would you know if the OE one is 12 Ah or 13 Ah, as there is a Varta 12 Ah/ 200CCA battery claiming to be the direct replacement for £37 + P&P at Tayna when I google the p/n you kindly provided. :)


There are some 13 Ah versions available also hence I questioned this. :)
 
Edit;
I’ve found a photo of an OE A2115410001 supplied by CVP Edinburgh, it seems the spec is; 12Ah 170A and branded FIAMM (made in Italy) :)
 
Yes, as above, this is usually the main battery. The front Aux battery tends to bring up a red AUX warning depending on how bad it is.
 
Yes, as above, this is usually the main battery. The front Aux battery tends to bring up a red AUX warning depending on how bad it is.
Ok so it specifically says AUX? Mine just says Battery/Workshop etc. No mention of AUX.
 
It's the main battery.

I'd get this on any of the W211 if leaving for a long period.
Connect to a battery chanrger/conditoner and you do not get it.
The aux. battery is isolated when the car is not being used. ;)
 
Thanks Pat but I get the convenience features disabled I thought this meant the Aux?

TBH - I left the car sitting for a month and it still started hence I assumed main battery was ok as I’d expect some difficulty starting otherwise?

No, aux is for the SBC, not used for other things.
 
Thanks chaps,

looking back... the main battery was last changed in 2013! So this looks the culprit.

Pat, sorry to be a pain, but do you have the details for the main battery please? :D all I can see on the invoice is 019 AGM
 
There are a few different ones.

100Ah one is A0009823308, last one I bought £100 in 2017.
 
When left for 1-2 days it’s fine, if you leave it sitting for a week or so it’ll start but come up with the error on the first start, ‘battery visit workshop’ and ‘convenience features’... then when you restart the car after a 10 min drive all errors clear!
If it is the AUX then you should experience this:
 

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