W212 E220 SE - Help Me Understand - Auxiliary Battery Malfunction

[ORB]

Morning guys, a little discussion and advice if possible?

My September 2014 E220 has been giving me the auxiliary battery malfunction warning now for probably 6 months, I normally just clear it with the steering wheel control and ignore. I assume this relates to the little battery under the boot floor next to the spare? I have tried charging it and it did not do a lot!

What does it actually do? I am guessing its something to do with the Start Stop as sometimes this is hit and miss?

Any heads up on where to get a cheapie replacement?

Any other pearls of wisdom?

Thanks

 

[malcolm E53 AMG]

I read it that all the auxiliary battery does is make sure you don’t lose consumables when the main battery is under heavy load. if the car is flashing up a warning time to change it

 

[ORB]

Would this not suggest the main battery is kaput?

I have no reason to think this as it start absolutly fine

Cheers

 

[malcolm E53 AMG]

I use a voltmeter to check both batteries should be 12.6V fully charged

 

[ORB]

Update:

Both batteries were showing correct voltage at rest, I decided to order up one of these, the problem has thus far gone away (has been fined for about 2 weeks now!)

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