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Discussion Starter #1
This is my first Mercedes and I am constantly learning about new ways to engineer automobiles. I love this car but this morning I received the "Auxiliary Battery Malfunction" message when I started her. This made me nervous so I performed quick search on the web and determined its ok to drive for at least today. During the drive the message text turned form Red to White (easing my anxiety). Now I have done a more comprehensive search and what I found there are 2 batteries and the location of the auxiliary could be either under the hood or below the glovie (always have to take web info with a grain of salt...); I think in my car, its the latter. Either way I know I can fix this my self but I need some basic questions answered.

1. Is this battery located below the glove compartment (as in the 2015 model year) and is the process the same (found video)?

2. Is it safe to drive the car if this message appears for like a week or more before replacing it?

3. I believe this battery is part of the start/stop functionality, what else does doe it affect?

Thank you in advance for any information provided. I hope as I gain experience with my C300, I will be able to pay it forward.
 

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Well... it might be "called" a battery - but it's actually a "capacitor" - here in the US there has been a least one no-charge recall/replacement - and several updates to that part.

I suggest to call your MB dealer 1st - with your VIN# - find out if you qualify for free replacement or fee update 1st ...

Keep the beat !
 

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As it happens I just replaced the one on my wife's 2015 C300 today.

It's definitely a capacitor type thing not a heavy little battery and it's located in the front passenger footwell on left hand drive cars.

Take the plastic panel out from below the glove box - one T20 torx screw near the door pillar, then clips.

Pull back the carpet to reveal a black plastic foot support type structure. It helps to pull back the passenger door trim piece to do get the carpet pulled back and try not to break the Styrofoam backing (guess who did...).

The black footrest panel is held in place by two M5 (10 mm A/F wrench) nuts at the botom and one more top right.

Take the footrest panel out and there's the capacitor.
 

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Discussion Starter #5
Well... it might be "called" a battery - but it's actually a "capacitor" - here in the US there has been a least one no-charge recall/replacement - and several updates to that part.

I suggest to call your MB dealer 1st - with your VIN# - find out if you qualify for free replacement or fee update 1st ...

Keep the beat !
Thanks for the info about the recall, this is a great suggestion. I have learned a lot more about this "battery" and went as far as purchasing the part. However once I ordered it, the message went away o_O... I kept the part because it's probably on it's way out anyways. Seems easy enough to do. FYI, if your a DIY kind of person, Amazon has MB parts at reasonable prices. The car is going to the dealership in October for sneakers (best installed price I could find with technicians I trust). Once again thanks for helping this newbie...
 

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Discussion Starter #6
As it happens I just replaced the one on my wife's 2015 C300 today.

It's definitely a capacitor type thing not a heavy little battery and it's located in the front passenger footwell on left hand drive cars.

Take the plastic panel out from below the glove box - one T20 torx screw near the door pillar, then clips.

Pull back the carpet to reveal a black plastic foot support type structure. It helps to pull back the passenger door trim piece to do get the carpet pulled back and try not to break the Styrofoam backing (guess who did...).

The black footrest panel is held in place by two M5 (10 mm A/F wrench) nuts at the botom and one more top right.

Take the footrest panel out and there's the capacitor.
Thank you for the DIY procedure, I also found videos on line that describe the same. Thanks for the help.
 
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