Ever had a Mercedes auxiliary battery malfunction issue?

[Ari]

I have a nearly decade old C Class that has started flashing up 'auxiliary battery malfunction' on start up. After about 1 minute or two it disappears. I've given it a really good long run at the weekend thinking maybe it's just a bit low, but it is still doing it.

I contacted my Mercedes dealer to tell them exactly the above, and how much please for a new auxiliary battery? Only to be told 'it could be a number of potential issues, we need to diagnose it first, £200 + VAT per hour please'.

Given that the battery is almost 10 years old, and the message is that the battery is malfunctioning, I'm very tempted to just swap the battery first, and go from there if the issue persists, just seems logical to me.

I wondered whether anyone else had had this issue and whether the battery had been the problem, or was it indeed something else?

[Scrump]

I had a similar warning on my E class. A new aux battery solved the problem.

[A M G]

Scrump said:

I had a similar warning on my E class. A new aux battery solved the problem.

Ditto.

[Gordon Hill]

My old E Class has been flashing up convenience functions not available for 16 months now. The car was stood for 3 months before I got it. I just ignore it now, just means I don't have heated rear windscreen and full blower power for 30 seconds or so after start up. Need a new auxiliary battery but I can't be bothered.

[f1nn]

Yeah, I had this on a 2014 W205 C Class I had few years ago.

Bought a new, genuine, Aux battery from a Mercedes dealer advertising on EBay, fitted it (under the front passenger footwell carpet near the bulkhead) and that was the problem sorted.

[MrC986]

If the OP can get the part number from Mercedes you can check it on Fleabay for alternatives although you'll need the battery spec/size to be doubly sure. My CLS started throwing up all manner of battery issues (now 10yrs old) and it was the battery. A new Varta one (it's a large battery as it's a single unit) was £155 from Tanya batteries delivered next day & probably about 1/3rd cheaper than from the dealer.

[Ari]

That's really helpful, thank you all!

There's a local and well regarded auto electrician local to me, I might give them a shout and see if they can fit one for me.