GLA auxillary battery

[keith of kent]

We have a 2017 GLA 1.6 petrol auto.
When its dark the headlights come on when the car is locked or unlocked but this feature stopped working.
I checked on the menus both on the steering wheel/ speedo display and also on the Vehicle settings on the radio/satnav display and the feature was turned on.
I now wonder whether the auxillary battery is failing so scanned the QR sticker on the B post , it shows tha main battery on the N/S of the engine bay and another in front of the steering wheel.
It's definitely not in the engine bay so is it up behind the dashboard? Is an actual battery or a capacitor?
I can take it to my trusted Indy but if I can buy a replacement from Tayna and fit it myself (as I have done on my E class) that would be more agreeable to my wallet.
Grateful for any help

 

[Diesel Benz]

How did you conclude the aux battery would affect this feature? Do main beams turn on at dark, perhaps a light sensor issue?

 

[keith of kent]

I haven't concluded it's the aux battery, it's just that I know from my E Class that it can cause all manner of problems. Yes the auto dip works as normal. It would just be nive to know if it's got an aux battery and where is it?

 

[Gallon]

Your car has a capacitor which EPC calls a "Relay Backup Battery" part No. A 000 982 20 23 it shows it's location on the passenger side dash on a LHD vehicle, so could actually be on either side on a RHD vehicle. When these start to fail you will get a warning to that effect on the dash. This component is only relevant to the Start/Stop function so should have no bearing on the fault you describe.

 

[keith of kent]

Thankyou. That is exactly the information that I needed