My wife had the auxiliary battery malfunction message today. The car is over 3 years old now so I assume it is simply time to replace it. Where is it located? Do i need to disconnect the main (starter) battery before replacing it? Any info would be greatly appreciated.

 

Use current OEM part # 0009829308 to search for cost effective compatible batteries See attachments for install.

 

Probably in the trunk and should be covered under warranty.

 

Yes, the auxiliary battery is in the passenger side of the trunk (labor intensive to get to ) and is for the stop/start function.

 

I had the same message on my 2015 S550. Took it to the dealer and it was covered under warranty.

 

LOL! Leave it to MB to have an aux battery AND have it in a hard to reach place for the tech

 

Just spent over 500 to replace main starter battery now i get the auxiliary battery malfunction.
I assume this isnt covered under CPO

Konigster just to confirm that model number you posted above does apply to the 2015 RWD S550? I found that part on fcpeuro but it says it does not fit your vehicle.

 

500?? Even my cls battery is half that.......are you working with a dealer??!

 

Yea this was through a dealer. Cost was 478.99 plus tax.

 

On my S63 AMG if you scan your gas tank lid there is a lil IRQ scan, when you scan it on iPhone it shows your battery’s locations says I have 3 battery’s one is 48 v and not sure on S550 but check to see if you have IRQ

 

Can you just let that auxiliary die without affecting anything other than the auto-stop-start function? If so, I’d say RIP!

 

Distronic is also inoperable

 

Can’t have that! Using Distronic has spoiled me. Thanks

 

It’s far worse than that. Yes the start/stop won’t work, and if you attempt to turn on cruise control you get a
nice amber warning about distronic disabled. However when you when you get to your favourite stop sign where you wait a long time and press hard on the brake pedal to turn on brake hold it fails... silently... and you get to roll out into on coming traffic.

You would think that a flaw that disabled a component of the braking system on the car might just result in warning for the driver.

 

Will they replace this under CPO warranty as well? My dealer said no...

 

No.... Its an easy DIY...