I've been using a CTEK on each of my batteries but I didn't put them on last week. Started the car this morning and got a message saying "Auxiliary Battery Malfunction". Car starts and drives fine. Have no idea but it might be the original battery so it may be almost 7 years old.

What's a good source other than the dealer for a replacement? Anyone know the model number?

 

Here's some info on the batteries for a 2019 SL450. Sorry I don't have an alternate part number for the Aux.

OEM Starter battery (AGM)
Pt No. A 001 982 82 08 26
Capacity 95 Ah; Start amps (CCA) 850 A
Vlies-Technologie
Dimensions: mm L353 W175 H190

Alternate Starter battery (AGM)
Varta SilverDynamic AGM 95Ah with OEM code (595 901 085 / G14 / 019AGM)

Aux battery (AGM)
A211-541-00-01

Good luck!

 

Thanks, hornethandler. I found the Auxiliary Battery, A211-541-00-01, for sale on Amazon and Autohaus AZ. Now I need to ensure I have the guts to try and install it myself.

 

This link may help... Not sure if it requires coding afterwards to remove the "error" warning.

Happy Holiday

 

After watching the video "Panzer Light" comes to mind.

 

Excellent video. Thanks for posting. I'm going to tackle this job after the holidays. Have my CTEK back on the auxiliary battery and it says it is now charged but I don't think it will hold it so I'm going to replace it. Will order from Amazon like the YouTube poster.

Happy Holidays to Everyone!

 

Post 39 and 44 of attached link may be of some help in removing the battery cage. I'm inclined to go with post 44.

https://mbworld.org/forums/sl-class-...t-guide-2.html

 

Looks like you’ve got some good guidance here.👍
Take your time and don’t use force.
The only thing I can add is be careful not to arc the terminals at any time. Remove negative terminal first as mentioned in the guides. And watch where you swing your wrenches! These cars are sensitive to voltage spikes/shorts and accidentally grounding the battery/circuits can lead to electrical issues. On some cars, as I’m removing and replacing the battery. Terminals can flop around or go in weird places/angles. If I find myself wrestling with a battery too much, I’ll temporarily wrap the terminals in electrical tape so they don’t strike the battery terminals until I’m ready to bolt them them up just to be safe.
That battery is pretty light, and access is decent. So you should be good. But just be vigilant with those terminals and what your doing around them.

Happy Holidays and good luck!

 

Good advice. It probably goes without saying but I'll add: when installing the battery connect the positive cable first.

 

I think I need to go shopping for a hacksaw blade.

 

I just used some medium heavy wire cutters. Was surprised how pliant the plastic was. Still don't understand the need for the plastic with more than half a dozen pretty heavy screws. I think you'll be able to this without much trouble. Good luck!

 

The excess number of fasteners is likely due to the “brother-in-law" effect. That is, the MB engineer who decided how many fasteners were required has a bother-in-law who owns a fastener factory.

 

I think I might have some tin snips. Maybe they will work. First, I need to order the battery. Anyone know if there is a source better than this one?
​​​​​​https://smile.amazon.com/dp/B0090ULA...v_ov_lig_dp_it

Added: I just found a Mercedes dealer in Tysons Corner, VA that will sell the OEM battery for $119 and ship it to me at no extra cost other than sales tax. I'm going to go with this option.
Update: Dealer said they cannot ship the battery so I'm back to the Amazon option. Also found an alternative that is supposed to be equivalent to the OEM battery for half the cost. I might try it as it is a local store and I can return it if the fit isn't perfect.

 

Had no trouble removing the battery as the case had already been removed before. I think it was to install the CTEK pigtail. However, the battery I purchased locally would not work. The size was perfect but the positive and negative terminals were reversed so the wires are not long enough to cross over and connect to the proper terminals.
I guess I will order one from my local dealer unless I can find one online. Found an OEM Mercedes battery online from Amazon. I'd like to confirm the date code but guess I will order it and hope for the best. The date code on my original battery was 29 14 so I think regular maintenance does help these AGM batteries last longer.

 

Thanks for the update.
Was the battery cage modified, i.e., tabs cut for easy removal?
Good luck!

 

I'm not sure. All I know is after I removed the 8 Torx bolts I was able to remove the cage with a bit of wiggling. I'm going to examine it closely before I reinstall it. I'm waiting for the new battery to arrive.

 

This is what we get for posting in that earlier thread about auxiliary batteries. Mine will probably check out next...I don't even bother to charge it myself. I just let the car do it on long-but-infrequent drives.

Btw, the M-B part number on my original 2017-vintage AGM auxiliary battery (dated 39/16) is A 000 928 70 08. It's rated at 12Ah, 170A EN, and it was made by Fiamm.

 

Same as my battery except mine is 2 years older. I'm still confused about whether or not the auxiliary battery is kept at a minimum charge level by using the underhood charging points.

Also, is it charged while driving? I am impressed by the long life of the auxiliary battery in my 2015. It has a date code that makes it almost 8 years old! I ordered the same battery as a replacement. Still waiting for it to be delivered.

I will continue to use a CTEK on both batteries as I will reconnect a pigtail to the auxiliary battery. Former owner installed it and I think it helped it last as long as it has.

 

Very informative video.
Thanks.

 

This video is excellent but the battery he purchased from Amazon is now $169.95. I found an Amazon vendor, Mercedes dealer, that sells the OEM battery for $139.00, with free shipping and no core charge.

 

New battery showed up today. Box was in terrible shape but battery was undamaged. Build date is 30 21 so that's a good start. Put it on one of my CTEKs and in about 5 hours it was fully charged. I plan to install it tomorrow if the garage gets above 25 degrees. It's been damn cold here in western MD.

 

Looking forward to hearing how the swap goes.
Full charge immediately after charge should be about 13.7 volts for the aux battery. It should settle in to about 13 volts after a couple of hours.

 

Did this at the dealer for not much over the OEM battery price....

 

My dealer wanted $175 for the battery and $200 labor to install. Once I saw how easy it was to remove the battery, I decided I could do it myself. Not just to save some $$ but for the experience. I just wish it wasn't so darn cold.

 

Success. The worst part of the installation once the cage is removed is getting the old battery out. Even though it only weighs 10 pounds it's difficult to get a grip secure enough to remove it as it is in a confined space. I ended up using vice grips to pull it out. I also only used 4 bolts to secure the cage around the new battery. That cage is very over engineered. I also reinstalled the pigtail so I can keep this battery maintained when the car is not driven on a regular basis. All in all it was not a difficult job but having had the cage removed previously was a big help as some of the tabs had also been removed. Thanks to everyone for their help especially the videos.