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?

[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.