Audible warning after battery disconnect, unable to solve!

[C250cgicoupe]

Hi I was hoping some members might be able to solve this problem, due to a shoulder operation I was unable to drive my car for 8 weeks and as a precaution disconnected the battery during this period. My car is a 2014 C250cgi coupe, after reconnecting the battery and driving the car roughly 10 mins I'm getting what I can only describe as a bleeping sound from the multimedia system, no warning messages. Sometimes after re starting the engine I can be driving for up to 30 mins before hearing it but it always returns eventually and once it does it will continue every few minutes. I have looked at all the settings for the nav. tel. stereo and have also done a factory reset and again today disconnected the positive battery terminal and grounded it to the negative terminal for 5 minutes but sure enough after reconnecting and driving for 30mins it started again, Mercedes couldn't suggest anything part from disconnecting the battery and trying again. It's really starting to annoy me, does anyone have a suggestion as to what the cause might be?

thanks.

 

[toteimerced]

Is there an auxiliary battery in the boot, like the E class? If so, it maybe the problem, try charging it and see if that works.

 

[C250cgicoupe]

Is there an auxiliary battery in the boot, like the E class? If so, it maybe the problem, try charging it and see if that works.

Yes there is, I asked this very question at the local Mercedes dealership if it could be related to the auxiliary battery in the boot and the reply was that if this was discharged I would see a message on the dash, but as you suggested I'll give it a go and try charging it.