2015 Mercedez Benz C300(W205) Auxiliary Battery FIX - IN REAL TIME 

Thanks so much for making this video. I had the auxiliary battery malfunction error this morning when I got in my car, so with the help of this video, I was able to take the part out and order a new one. Couldn't have done it without you.

Mario all your videos are top notch. I realize they all can’t be live but you do an excellent job with them thank you much for sharing 👍👍👍

Thanks this was very informative! It's 15 minutes for those with the tools on hand and some experience removing and putting back the plastic panels, but for the rest of us it'll probably take an hour or two, including the time it takes to run the nearest Home Depot to get the tools.

Thank you for doing this! Easily found and ordered the part next day on Amazon then easily switched it out in 20 minutes. $70 and 20 minutes of work at home vs $700 and leaving the car at Mercedes all day. That's a win in my book! Appreciate you!

This video was very helpful. I was able to do it in 15 minutes and hardest part was moving the carpet. Thank you for posting this video

I did the replacement on a 2016 C-300. The job went super smooth thanks to your video. Thanks Bro!

Thank you so much for this step by step real-time video. I just replaced the voltage regulator per your video. Saved me a ton of money because the dealer was going to charge me almost $500 to do it and I did it myself having only to purchase the part for less than $100. I did not have a computer to reset the code, but once I replaced the regulator, the error message on the dash went away. Hopefully this takes care of my issue for a while. My car was a 2015 C300 4Matic. Awesome video. Saving it in my favorites!!

I have a 2016 c300... bought the part on eBay for $60 bucks.. changed it myself using this video! The auxiliary malfunction message disappeared immediately. THANK YOU thumbs up 👍

Excellent video Mario, its pretty awesome seeing real time repairs. You have to be skilled and confident in your abilities to do that. Not everything is a 30 second fix. I'm always looking forward to what's coming out next.

You have saved my life!! My daughter has her driving test tomorrow here in the UK 🇬🇧. Last night I realised that if there are any fault warnings, then the examiner will refuse to let her take her test in it. The cost including Labour costs about £300 + VAT (Tax). So I followed your instructions and bought a Auxiliary Battery, fitted it and had the garage do the code. All done at )75 + VAT. Real time video is much better, so keep them coming. Thanks again Francesca

Great video. I replaced mine in 20 minutes without an issue thanks to you. For those wondering I have a RHD 250d and as you would expect the auxiliary battery/voltage converter is on the other side.

Thank you for showing it to us, Super Mario! Saw it, understood it, did it! Consumers become fixers ... need more of that. Herzlichen Dank from Zurich, Switzerland.

thanks mate. this is the second time it failed so replaced with non genuine unit and managed to do it all by myself thanks to you.

Another fantastic video, Mario, Thanks for the time and effort to produce excellent tutorials, well appreciated, Bless 🙂😇

It got me too! (W205 Juni 2014, ...004). With that video and a skillful hand it was fixed very quick. Thank you!

Thank you so much from Germany! I needed about half an hour because simple mistakes and slow working, but it was really easy! In this half hour I saved about 400 Euros. You made my saturday.

Good job mario! And not editing this allows everyone to see the struggles we face getting these cameras into areas that we barely fit in ahaha! I’m liking that Launch too!

Thank you Mario. Your detailed video gave me the confidence and everything I needed to know to replace the aux battery (capacitor). The dash was indicating “Auxiliary Battery Malfunction.” Please keep up the great work!

Thanks for the vid. It's impressive how complicated mercedes made the car. It literally has a second battery buried deep behind two covers.

Great step by step video.. made it simple to switch it out. The only thing that gave me an issue was the first cover. I bent the hook on the back a bit. Other than that a breeze.. thank you for posting.

Great job explaining! It's probably the best I have seen so I had to subscribed to your channel.

Just copied your instructions and it was easy. I’m in the UK and the part from Mercedes was £110. Nice to save a few hundred more in labour by not taking the car into Mercedes. Many thanks for the video!

Excellent video. Great communication. Very professional. One of the best in North America.

Great vid, many thanks - it worked for me. The hardest part was holding the carpet down, but no need to slit it, it can be kept out of the way to get the lower two 10mm nuts.

Thank you sooooo much for this video!! You’re a great teacher!

I have a 2016 MB C300 and the "Auxiliary Battery Malfunction" popped up an hour ago after I started the ignition. I panicked! Anyway, I took a chance and drove the car to the park to walk my dog. I googled for an explanation and found this RU-vid video. I am not a mechanical person and I hate fixing anything related to cars, so I think I'll just take the car to a mechanic. Thanks for the explanation and demonstration anyway, Mario!

Thanks for the video, always good to see you working.

On W205 Mercedes 2017, I had same fault code as you changed the small baterry like you did.. but i had stil the same problem and same fault code like you.. then i changed the 12V battery under the hood and it worked!

I’m loving your real-time videos. Most guys edit for time and it makes things appear to always go smoothly and in short time. The struggles of dropped fasteners are real! I’m also happy to see some of your Harbor Freight tools in action. All those people who don’t think HF stuff is useful in a production environment amuse me. I swear by their impact sockets and the Earthquake line of cordless tools. I abuse them daily.

Thank you for making this in real time. These aux. battery malfunctions are so annoying as they block your screen from driving out from where it happened. In my case my phone map malfunctioned, getting me lost in residential, at night, during -44 frigid weather!! What an annoyance!! Now that I'm at home, safe & warm, it's nice to know I can prevent this from happening again. My question is will changing this aux. 2nd battery prevent these light & other accessories that drain power from my car's battery since I do mostly short distance trips at periodic intervals? Love seeing every step with real good lighting & proper tools for a quick swap out. 👍👏👏

nice one Mario. I have done one of these last month and a motorbike style battery on another Mercedes this week. seems they are common! keep up the good work buddy

Thanks for the video, this really helped me save a lot of money versus taking it to the dealer to fix! Next time u make a vid please include the part number in the description so I don’t have to keep rewinding and pausing the vid to be able to see it!

Hi, thanks for doing this video. Do you know if the procedure / part is the same for a 2016 C63?

I found this super easy to replace by removing the carpeting from the passenger well, which requires unsnapping the plastic trim on the right of the footwell. Access to the panel is then easy and doesn't require unscrewing the panel above.

Thank you! You have given me the confidence to do this myself.

Great video, got the parts and followed the video, the only issue i had was removing the carpet but otherwise done in about 30 minutes. Problem now solved, Thanks

Thank you very much for this video, it made the replacement very easy for me. The notification I had on my dash was "auxiliary battery malfunction". Dealership wanted $170 for diagnosis and then parts and labor, would have worked out to be over $500 total and got away for $130.

Thank you. That helped a lot. Mercedes quoted $450. Did it for $138 my self. Appreciate it.

Thanks my friend. I have the 3015 c300 where the steering wheel broke in the up position. I can hear the motor running.ive read in the MB forum it's the "dog bone's. Can you show us how to replace it?

Thank you! The fix also exactly applied to our 2016 GLC 300...

@Mario, i have a 2013 C250 Sport. It gave me the battery light yesterday then cleared on its own. Today the light came on again and the car turned off my stereo to save pwer i assume. I had the battery and alternator checked and the battery is good but the reading on the alternator said low voltage. I didnt get the dashboard message that says to stop the car and keep running. Could this be the Auxiliary power issue you had here or is this issue solely with the Alternator?

Thanks a lot Mario for your help, very good video !

Yes, i think that videos like this, help us to replace some part of our car, because on the dealership they charge a lot of money, even thought if the part is too cheap.

Do you know if for 2015 s65 sedan this voltage controller is located in the same place? I checked by vin nr it’s the same part number. Thanks.

I enjoyed it. Thx for sharing Mario 👍

Despite me changing to a brand new aux battery from purchased from Benz dealer. "Aux battery malfunctioned" remains on my dashboard for 9mo now on my 2010 gl450. Any suggestions?

Hi, my media centre cuts off for a few seconds and comes back again while i’m driving, also freezes the radio volume and few other things, if i restart the car can fix the problem but for short period of time. I asked specialist and he recommend to change the Aux battery, will this really be the case? I have no messages and no red lights on the screen. Do you recommend to change the aux battery as well?

Thanks for the video, the error disappeared once I changed the Voltage Converter Module, but on the screen the ECO light does not show up anymore and it does not start/stop even though the switch for ECO in the center console is on and lit green. Does it need some kind of hard reset. Thanks again

Does the part that you acquire goes with all the models of the c300 2015 and where is the best place or site to get it?

Perfect instructions. Took me no time aside from having to go buy a 10mm deep socket. :D

Best video I found. Thanks!

Hello Mario, greets from Aachen in germany, I have here a S205 C300 hybrid from one of my customers, and the electrical vacuum pump received only 9,5Volt at nearly no current, so does the pump not work. Is the front sam left side of the component you changed in this video? Fuse 30 and 118 in the front fuse box do have the same only 9,5Volt. Any ideas? which code reader do you recommend?

Thank you for your time in doing this video.

Where does the ML350 2015 auxilary battery locate? Is it in cargo? or is it underneath the front passager seat?

Brilliant, took me 20 minutes. Thanks

Hi great video! Changed mine but unfortunately message still coming up with fault code buffer battery of electronic ignition lock has a malfunction. Have you experienced this? Any help would be greatly appreciated

When you install the new battery will the, stop vehicle message go straight off on its on?

GOOD ONE MARIO , THANK YOU .

I have done this but sign still comes up stop vehicle shift to p leave engine running does and also my eco start stop has not been working for a while does it mean i need to replace my main battery too?

any idea what that could be if I’m getting a red tripple battery symbol on the dashboard malfunction see owners manual . On my mercedes 2018 reg . C200 petrol ???? Is that the same thing I need to change like many of you done ? I’m talking about auxiliary battery voltage converter?

Hi, i have an w213 2016 and i want to change my auxiliary battery. It just unplug the old one and plug the new one or i need to make an diagnostic or stuf like this?

My 2016 Mercedes Benz B class electric car has the same issue does he have it auxiliary battery too ?

Just replaced mine thanks to you. Appreciate it

Unbelievable the things they put in cars and where they put them where do you go to find the location for modules. We have Mitchell at work but I have trouble navigating through it, of course I’m 61 years old and have only been learning this stuff for a little while thanks for the info and great videos keep them coming they’re a great help to me I’m going to try to make super Saturday

Will the car still function with this light stop the car from starting or will it stall while driving or while the car is idling ?

Love it when I go to jump these cars to find the battery covered in water, I often ask the customer if they tried to fill up the cells and if they though more would be better.

Does this fix the auto stop start ? I got the message on the cluster waited a long time now the instrument cluster goes black when I turn on the car so I just ordered it

Out here doing the Lords Work! Thank you!

Just did this!👍 Hardest thing was to put the first foot well plastic cover back in when I was done.i was there for like 15 mins.in the end it just slides right in

Thanks for information and video. I really enjoy watching it. A A from Karachi Pakistan. 👍

Hi, Will this method be the same for a GLC300?

Good video. Do you have the electrical diagram of this aux battery? To which wires is it connected (like 87 maybe etc)> And can you give me the capacitance and voltage (surely must be over 14.4V) rating of the four capacitors (in microFarads/uF or miliFarads/mF or even if it is in the Farads/F range)?

HOLA MARIO. NECESITO SABER DONDE SE ENCUENTRA LA BATERIA AUXILIAR DE UN 2011 MERCEDES BENZ E350. GRACIAS.

Great video. Just had this problem and your video was super helpful. Not to nit pick but, you installed the cover over top of the removable carpet :)

Hi Mario, Thanks for the video :) Please do you have a link to the part? Thanks!

I have a 2018 glc 300 suv not the 4matic would that second battery be in the same location

Thanks for the video. I was suspecting this battery because the car does not start stop, but i think it is the bigger battery on the hood. Even with start stop enabled, car disables the function. Thats actually nice, but there has to be some reason why it does so..

Good one dude. Thank you for every details you went through.

Did same error message come up till your cleared it after installing new part?

I also replaced the small battery like in your video but after mine sais error back up battery then.. it sais stop car leave engine running.. i have the same error code as you had

Hi, my 2016 c205 c220d music is messing around, there is no wound coming out from speakers, but I can see music playing on the screen..done a diagnosis with the xentry star and it says my command unit fan 2 malfunction and also my rear view camera doesn't come on anymore, and also says all four speakers have short circuit too..any ideas why or how to resolve. Would really appreciate any ideas. Thanks

Thanks brother. But how do u reset the warning message/code ?

Good Video, thanks for the help - was almost as easy as you suggest and the issue was handled for $150 bucks. (The plastics were not at easy - had to fight with them a bit - thanks :)

Mario there are codes that accompany the low battery, did you happen to tag them in the description?

I just got this error code this evening. Seems like a pretty simple replacement, but do I have to take it to my mercedes dealer to clear the error code or will it clear itself?

I have same issue in my c300 2015 how much is going to cost me to fix this issue?

Great vid thanks for stating the bolt sizes!

Very helpful, thanks!

Great video, thx for sharing.

Hi mario listen i have a 2018 mercedes-benz C300 2.0l i change the auxilary battery and the stop vehicle leave engine running still on

Hi - I have a UK Right hand drive c250, Will my Aux battery be in my passenger footwell - that is the left hand side if you were sitting in the car? Thanks in advance. Great vids.

Cool, do I need to disconnect the main battery before I attempt this?

Mario, thanks you soooooo much! You are the man!

Followed the instructions thanks. There's a third nut to be undone you were missing. Also you don't need to have the code/warning reset. Mine went away after the first drive.

Thank you so much. Just fixed mine by myself. Dealership was asking for $450

Repleacement with or without started engine ?

How many miles we can drive with this code on I have same issue

Hello where u get the part from ?

Good video Mario. Cheers from Jay from Mauritius

Thank you very much. Helped a lot.