W211 Battery visit workshop/convienience function warning

[Oli]

My car has been parked for a few weeks and when it has been driven after it has come up with convienience functions unavailable then they have come back after a while, then the car wouldn't start, a few hours later it did on its own with no jump cables needed.
I've replaced the battery and the car is starting but still sometimes get a battery visit workshop message although the car seems fine, sometimes it seems to idle not quite level the revs will fluctuate by 100 rpm or so.
A quick google search seems to say theres an Aux battery which might need replacing too to cure the problem?, is this common on the W211?, battery warning charge light is not staying on so I assume it's not an alternator/charging issue?, all belts look to be in place still.
Has anyone else had an aux battery fail? and know the right part number to replace it, I understand it's under the pollen filter on the right hand side of the car.

 

[shorty]

The aux battery could need replacing espacilly if its the orignal battery . It could be worth putting the battery on a trickle charge over night as this may sort the problem

 

[Oli]

Thanks, I'm going to try replacing the Aux battery too, if the alternator had failed I would get the red battery warning light on the dash like on most other cars I'm guessing?.
Does anyone know the part number for the Aux battery or better still the specs of it?, as I gather it's similar to a motorcycle battery so easy enough to source.

 

[bostonmj]

Check out the thread Battery Convenience (URL Below) - a well versed question on this and other forums

http://www.mbclub.co.uk/forums/electronics/101526-battery-convenience.html