misonido

Hi all, new to the forum and need help locating the Auxiliary battery on my 06 R350?!?! I've located the main battery under the passenger seat and see a fuse block on the cross member behind the battery but do not see where the Aux Battery is. Can any of you guys help?
Thanks in advance. Cheers!

misonido

Found it!!! it's under the right passenger footwell in case any of you dare to replace it yourselves... will have to remove door moldings and pull up carpet to get access to and remove the panel (not battery cover but actual false floor)

D_D

How does the Aux battery work? Is it possible to not drain your main battery while the car isn't running?

MBtech1098

The auxiliary battery serves only one purpose, and one purpose only. It engages "park" position in the event that main battery voltage fails.

hcetzneb

+1

hcetzneb

Just make sure that the batt is being charged.. Ive seen a buch just go bad but ive also seen some go bad from the front sam stops charging them..

Easy test is to monitor it with a meter and make sure you see 12v at some point.

Or if you have access to a sds diag system you can activate the charging of the aux batt. and then check.

vshahid

Here are some pictures to show the battery, its location, and a generic replacement from batteries plus.
I strongly recommend when making this replacement, to permanently relocate the aux battery next to the main battery by creating a pair of extension wires about 1.5 foot long and pass them from the current location, going under the carpet to the new location next to the main battery where there is ample room for a standard UPS battery like a 1270. Note: You'd have to find a way to anchor whichever battery you use.
Pull off the door moulding and foot panel

Push the Passenger footwell plastic panel out of the way without cracking or completely removing.

Remove the 4 plastic nuts holding down the fiberglass panel and lift it. It rests in a slot towards the front. Nuts are only on the back and sides of it.

And here is the battery held by 2 similar plastic nuts one towards the top and one in the deeper bottom side. Easy to get to but not easy to see.

Original battery compared to a replacement battery. 10mm wrench for size. The replacement happened to have its terminals the other way around, but the existing leads were equal in length so it was no problem hooking it up.

foxear77

Many thanks to this site, I have just resolved my issue I had with my command centre failing to respond to any operations, ie, no phone, no sat nav, no cd player, nothing! although I could change only radio stations, and volume on the steering wheel controls, anyway, having scrolled through this site and reaping info, I finally found the main battery tucked away under the passenger seat, ******* to get at, but managed to expose one terminal, disconnect it for a couple of minutes, then reconnect, and hey presto, a result with everything working again. I have recently purchased an 'R' class, 2007, 320, hope this helps others out there. Regards,, Jack.

ODIOUS

Are you saying this auxillary battery is connected to the COMAND system too?
And it bypasses the fuse in the fuse box?

foxear77

HI, ODIOUS, I´M SORRY, CAN´T ANSWER THAT, BUT I SEE ONE OF OUR CHAPS ON HERE SAYS IT IS PURELY THERE TO POWER UP THE ´PARK´ WHEN MAIN BATTERY IS DEAD/DICONNECTED, I´M NEW TO THIS VEHICLE, SO ALSO AM LEARNING!!

josworth

No, if you read that post again, he disconnected the main battery by accessing the battery box under the passenger seat. The Aux battery is located under the front passenger foot well with the main battery behind it.

Actually, those posts are a little misleading. It is there to allow you to shift it out of park in the event of a total power loss. The transmission does not have any linkage so to speak. It is controlled electrically. The Aux battery allows a service person to get the vehicle in neutral to allow it to roll or be towed if you have no main battery power.

foxear77

Thanx for that info, Josworth.

samnt650

Just replaced my aux battery. The "aftermarket" part number is CA1212, or UB1213. The battery dimension is 4" x 2" x 2". Yes it is very tiny...

efzauner

I wonder if its good to change this battery after a few years anyway, certainly at the aftermarket cost of $20 or so.

bubarsmith

Thanks for this thread, no MB dealers near me(over 160 miles away) and almost $200 for replacing an $11 battery is crazy. Btw, I had to remove 5 nuts to get the fiberglass floorboard up. Oiled them putting them back in so that the hard to reach ones went on and hopefully com off better in another 11 years.

MattZone

Hi Everyone, I enjoy the posts and info. As a way to contribute, I recently changed out the auxiliary battery and took a few pics. I moved the seat all the way back and removed the passenger foot panels. The battery sits in a bracket underneath the carpet and board. I did not have to remove the seat at all and the battery was relatively easy to get to. Hope this helps!

MPDano

I just replaced the main battery under the seat, it was 6 years old. I am still getting that little warning battery light, usually first thing in the morning, but it eventually clears out the light. Would this little Aux battery under the footwell be the cause of this? Great thread and pics BTW.

Leo

MattZone

The warning light was still on for me too (it would sometimes go away during the day). After replacing the Aux battery, I had no further warnings.

MPDano

Excellent! Thanks for that.

diesel88

MattZone

Andy Y. Liu

I replaced the battery under the carpet, and still getting the warning light. The battery measures 12v dc and no resistant at the positive/negative lead from the SAM. Is there a relay between the battery to the SAM? I checked with car started.

C230 Sport Coup

Did anyone do a scan with iCarsoft or other Mercedes scanner and see if there's an error that needs to be cleared?

ODIOUS

Im actually surprised these SLA batteries can last 10+ years. These are the same type that go into my UPS and those dont last more than 2-3 years.

Replacing them with consumer grade SLA will likely mean we'll be replacing these batteries again in a few short years.

Vida01

car will start but will not move out of park?