Nice Ride

Its the amps that matter... Volt meter will not work. If its over 3 years old, replace it. Average lifespan of those batteries are 3 to 5 years.

vinnybenz

Hi 'whoover', I recently took my 2018 S560 to the dealer who did a Xentry diag and showed battery at 11.8 V. So based on your comment that the batteries are essentially replaceable at 12.4v.. I thought I would confront the dealer to change the Aux and main battery. He then did another Xentry diag and claime the voltage was 11.8v and that was within the MB range of 'good', that range being, 11-15v..
Do you or other members have a true replacement voltage for each of the 'Main' and Aux batteries?

juanmor40

I had the issue a few months ago on my 2014 E350, the aux battery voltage (when disconnected) shows 12.8xV after trickle charge, and even after a few rides. The message still showed up.

While shopping at Samsclub, I asked the auto department what battery tester they had, and it happened to be one of those Midtronics one (which MB dealer claims they use to test these batteries), even though the voltage passed, the health status (CCA available) was dismally low, so I replaced. Trouble free since.

akoustic

Thank you this helps a lot! I bought a battery tester off of Amazon (will come in handy for my other cars in the future) but looks like it’s time to replace. Will report back for everyone!

Jud Chapin

Car batteries need to be tested under load. Just checking voltage doesn't prove anything. I've seen batteries tested for volts only read 12.8 volts but when a load is put on the battery, the volts drop to 8 or less, hardly enough to support a car's electrical system.

akoustic

Update: Battery tester arrived today ($20 from Amazon) checked CCA on the aux battery and it was very low at only 28CCA. Voltage checked out fine at 12.89v. Will be visiting Benz dealership tomorrow to buy a new aux battery.

amgs63dxb

Looks like mine died today too... or at least the error shows up in the morning (no errors after I restart a car after a few mins of driving). So I got a replacement aux batt from the local store, but they said the old number was replaced and they only offer A0009829608. I'll fix it over the weekend, I guess...



Things that don't work when error is on:
1/ auto hold (inconvenient)
2/ distronic plus (speed limiter works so I don't mind)
3/ eco (engine always on)
4/ parktronic does not seem to work (which is funny when you don't know), but now that I checked the picture above - it was actually working when I was leaving the driveway (most likely gets disabled after the error shows up)

FS Gray

My AUX battery acted up 1 year ago but I trickle charged it on the front battery posts and all worked well for 1 year. Then it started to do it again. My wife drove about 300 miles before the cruise worked. By the time I drove it back a week later same thing happened and around 300 miles everything worked again. I have a new battery to put in it tomorrow but it was a challenge finding one at any of the MB dealers.

Jud Chapin

Does the car sit a lot. If so, this will run the aux battery down. I had no trouble finding the battery at MB. I paid $125 out the door in West Palm.

It's a job replacing this battery. Plan on a least a couple of hours if it's your first time doing it.

juanmor40

Here is a video in case you want to tackle it yourself

akoustic

On my w212 facelift it took less than 5 minutes to change out the battery in the trunk. Honestly I tried everything… trickle charged the main battery then trickle charged the aux battery to full but in the end it just didn’t have enough juice. All in all spent $180CAD tax included for a new aux battery. I could have gotten one from Amazon for $55 but I thought what the hell… anyways problem solved. 🙂

amgs63dxb

I wish it was only 5 minutes in pre-facelift W222 ;-) The video above does not mention how painful it is to move the fuse box and surprisingly the car does not seem to have valved exhaust module, that sits there in the way also... the guys is just like "move the fuse box and now pull out". With bleeding hands and pain in the back - after 20 mins I managed to extract mine and replace... Original battery dated 2013 (!). So 8 years - not bad, considering that main battery died a year ago and it had 2016 embossed on the sticker...

Jud Chapin

Yikes...At least the fuse panel doesn't have to be removed on the S coupes. Still a PITA job. Why MB builds cars this way is beyond me. The battery on my '02 CL500, there was just 1, was located on the rear right side of the trunk for easy replacement. The main battery on my '16 S Coupe is located in the trunk just behind the rear seat. Have fun replacing it. I requested a new main battery when I bought this CPO. I didn't know about the aux. one or I wold have had them replace it to.

MurrayG

Just to reinforce / clarify the comment above, I checked my 2014 S550, and indeed charging the main battery with my maintainer via the charging posts under the hood (bonnet for you in the UK) does indeed also charge the aux battery.

See image below. The charger was attached to the main charging / jumper posts under the hood when this picture was taken, and the vehicle was off. The reading before attaching the charger was 12.8. Once the charger was attached and kicked in, both the main and aux battery showed roughly the same charging voltage.

Certainly in my vehicle, there is no need to attach a second charger directly to the aux battery.

Jud Chapin

Good to know...

MurrayG

I should also add that removing all the various trunk liners and detaching the fuse block to get at the AUX battery was not a big deal at all. It probably took all of 30 minutes max (probably less) to get it all removed. I do have the help of a nice set of car trim removal tools from Amazon - I can't believe how I lived without these before - they are wonderful ( ).

So for any of you wanting to replace your main or aux batteries, I would not hesitate. I am replacing both as a preventative measure as they are original and are thus about 6 - 7 years old. Plus I am pretty sure doing both myself is saving about $1,000 CDN.

All the best -

autoluke

A bit off topic, but is it mandatory that only a Mercedes battery should be used as a replacement ?

MurrayG

Not at all. In fact you will find that most people on this message board who have replaced either their main or aux battery (myself included) simply use any good quality battery. Just make sure it is the right type and size.

Merserybenze

I read through this chain but can’t tell what part I need. Anyone help with what and how? 2018 S450 4Matic. “Auxiliary battery malfunction” error this morning. Thanks!

konigstiger

Have dealer check vehicle master inquiry (VMI) to see if your VIN is included in attached Service Campaign, may resolve matter. If not and auxiliary battery needs to be replaced shop current MB part # 0009829608, see attachments.

Merserybenze

Thanks!!

seamus2154

I just replaced mine this month. 6 years. I'm ok with that. Bought through Rockauto, Excide was the brand. Fit perfectly, was exactly like stock. I will agree with above, it was a PITA. But it was not hard. Set up a blanket and stayed organized, and was in no rush. Came out perfect. Removing that whole panel was ridiculous design for a maintenance Item.

Merserybenze

I dismantled everything. Pita but took about 20 mins. Picking up OEM Battery from MB tomorrow. Mine lasted 5 years. Saw the main battery under there too. Same age. Florida car. Should I change that too or wait?

seamus2154

The MB main batteries last pretty long. I am in Fla also and owned many MB. I am at 6 yrs and it spins up quick. Pay attention to your start up as it does usually let you know its slowing. I have read of many getting 6-8 years on a MB battery. In my experience MB batteries last the longest and VW and Gm are sometimes 2 years!! they are a crapshoot, because I have had GM go 5.

Mike_Metal

My auxiliary battery died in 2.5 years. MB replaced it under warranty. While it was not functioning many ofMB UX and Distronic functions were not functioning, driving without cruise control for 300 mile was an ordeal.