Does the Auxiliary battery malfunctioning stop the car from starting or do I need a 12v battery too

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Robwalls

New Member
Joined
Apr 3, 2024
Messages
6
Location
London
Car
C350e
My c350e 2016, has been sat on a driveway for a bit too long than I’d have liked. I went to start it up and it was totally dead.
So after I jumped it, it started perfectly, with a warning on the dashboard stating auxiliary battery fault.
I wouldn’t have thought this would affect the car from starting. But I don’t really know.
Do you guys think I need a new 12v battery aswell as an aux battery
Thanks!
 
You really need to test both batteries and see how many volts they are holding when fully charged for a start.
My C Class is September 2016 and it doesn't have an aux battery, it uses a capacitor instead. Earlier models did have an actual battery, do you know when yours was built?
 
You really need to test both batteries and see how many volts they are holding when fully charged for a start.
My C Class is September 2016 and it doesn't have an aux battery, it uses a capacitor instead. Earlier models did have an actual battery, do you know when yours was built?
Mine is 2016 also
 
I bought a cla35 in late February from a merc dealer. I saw on the dvla tax site that it hadn't been taxed for several months so I thought it had been sat somewhere and when i went to view it, the battery was dead and the young salesman said he would get it sorted. When i collected the car, all seemed fine but on the way home, the auxilliary battery malfunction message came up on the dash and i'd already noticed that the 'hold' function wasn't working. A quick google and the 'hold' function depends on the auxilliary battery.
I took it to my local merc dealer and they put a new auxilliary battery on and they also said it needed the main battery as well so it had both replaced.
I read online that if the main battery is losing charge, it relies on the auxilliary battery but the dealer had left it standing for so long, the auxilliary battery had failed as well.
Perhaps replace the auxilliary one and test the main one.
 
I bought a cla35 in late February from a merc dealer. I saw on the dvla tax site that it hadn't been taxed for several months so I thought it had been sat somewhere and when i went to view it, the battery was dead and the young salesman said he would get it sorted. When i collected the car, all seemed fine but on the way home, the auxilliary battery malfunction message came up on the dash and i'd already noticed that the 'hold' function wasn't working. A quick google and the 'hold' function depends on the auxilliary battery.
I took it to my local merc dealer and they put a new auxilliary battery on and they also said it needed the main battery as well so it had both replaced.
I read online that if the main battery is losing charge, it relies on the auxilliary battery but the dealer had left it standing for so long, the auxilliary battery had failed as well.
Perhaps replace the auxilliary one and test the main one.
Hi,
Thanks thats very helpful. I think that may be what has happened to mine. I’ll give it a check and get them replaced!
 
I replaced my main battery fairly recently because of starting issues, the aux one is only used for stop start and hold feature, mine has been dud for 3 years, don’t need it really as always disable stop start as it’s a pain.
 
Hi I have a 2013 c205 that has both batteries. Tbh because of age I replaced them myself with batteries from GSF prices from a year ago 15min job to swap
Also replaced the aux which from memory was about £65-70 for a YUASA with a 2 year warranty I imagine you could do the pair now for £250 half hour to fit the pair with a decent socket set.
DRBDA115 /115 AGM Stop Start Plus Battery - 3 Year Warranty1£138.59
 

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