Mercedes-Benz W205 Auxiliary Battery Replacement DIY (Mercedes-Benz C300, S63 AMG, C63 AMG, & More)

►One of the most common searches on the Mercedes W205 is related to the Mercedes-Benz auxiliary battery.
If you own a Mercedes-Benz W205 with electronic gear selectors or the eco start-stop function, your vehicle has something called a voltage converter, commonly referred to as the auxiliary battery. If you notice an auxiliary battery error message on the dash telling you to shift the vehicle into park but leave the engine running, or if you have the auxiliary battery malfunction message, there's a good chance that this is the part that needs replacing.
If you have to replace your Mercedes-Benz main battery at any point, it is wise to replace this auxiliary battery at the same time along with it. This is a very straightforward job that does not require the use of any special tools. Kyle Bascombe, FCP Euro's Mercedes-Benz Catalog Manager, covers taking out the old battery, assessing the failure point, swapping in the new one, as well as inspecting other potential failure points if your auxiliary battery has burned up.
Shop the parts used in this video:
Voltage Converter: www.fcpeuro.com/products/merc...
Index:
00:00 - 02:00 Intro & Tools Needed
02:00 - 05:30 Carpet, Trim & Kick Panel Removal
05:30 - 06:45 Auxiliary Battery Inspection & Removal
06:45 - 07:20 New Auxiliary Battery Install
07:20 - 12:15 Kick Panel, Trim & Carpet Reinstall
12:15 - 14:30 Fuse Inspection
14:30 - 15:03 Thanks For Watching!
#fcpeuro #W205 #Mercedes
This video applies to the following vehicles:
Mercedes-Benz S63 AMG
2015 Mercedes-Benz S63 AMG Base 5.5L V8
2016 Mercedes-Benz S63 AMG Base 5.5L V8
2017 Mercedes-Benz S63 AMG Base 5.5L V8
2018 Mercedes-Benz S63 AMG 4Matic 4.0L V8
Mercedes-Benz S65 AMG
2015 Mercedes-Benz S65 AMG Base 6.0L V12
2016 Mercedes-Benz S65 AMG Base 6.0L V12
2017 Mercedes-Benz S65 AMG Base 6.0L V12
2018 Mercedes-Benz S65 AMG Base 6.0L V12
Mercedes-Benz C400
2015 Mercedes-Benz C400 4Matic 3.0L V6
Mercedes-Benz C300
2015 Mercedes-Benz C300 4Matic 2.0L L4
2015 Mercedes-Benz C300 Base 2.0L L4
2016 Mercedes-Benz C300 Base 2.0L L4
2016 Mercedes-Benz C300 4Matic 2.0L L4
2017 Mercedes-Benz C300 4Matic 2.0L L4
2017 Mercedes-Benz C300 Base 2.0L L4
2018 Mercedes-Benz C300 Base 2.0L L4
2018 Mercedes-Benz C300 4Matic 2.0L L4
Mercedes-Benz GLC300
2016 Mercedes-Benz GLC300 4Matic 2.0L L4
2016 Mercedes-Benz GLC300 Base 2.0L L4
2017 Mercedes-Benz GLC300 4Matic 2.0L L4
2017 Mercedes-Benz GLC300 Base 2.0L L4
2018 Mercedes-Benz GLC300 Base 2.0L L4
2018 Mercedes-Benz GLC300 4Matic 2.0L L4
Mercedes-Benz C63 AMG
2016 Mercedes-Benz C63 AMG Base 4.0L V8
2017 Mercedes-Benz C63 AMG Base 4.0L V8
2018 Mercedes-Benz C63 AMG Base 4.0L V8
Mercedes-Benz C63 AMG S
2016 Mercedes-Benz C63 AMG S Base 4.0L V8
2015 Mercedes-Benz C63 AMG S Base 4.0L V8
2017 Mercedes-Benz C63 AMG S Base 4.0L V8
2018 Mercedes-Benz C63 AMG S Base 4.0L V8
Mercedes-Benz C450 AMG
2016 Mercedes-Benz C450 AMG 4Matic 3.0L V6
Mercedes-Benz GLC43 AMG
2017 Mercedes-Benz GLC43 AMG 4Matic 3.0L V6
2018 Mercedes-Benz GLC43 AMG 4Matic 3.0L V6
Mercedes-Benz E300
2017 Mercedes-Benz E300 4Matic 2.0L L4
2017 Mercedes-Benz E300 Base 2.0L L4
2018 Mercedes-Benz E300 Base 2.0L L4
2018 Mercedes-Benz E300 4Matic 2.0L L4
Mercedes-Benz C43 AMG
2017 Mercedes-Benz C43 AMG Base 3.0L V6
2018 Mercedes-Benz C43 AMG Base 3.0L V6
Mercedes-Benz S550
2017 Mercedes-Benz S550 4Matic 4.6L V8
2017 Mercedes-Benz S550 Base 4.6L V8
Mercedes-Benz E43 AMG
2017 Mercedes-Benz E43 AMG 4Matic 3.0L V6
2018 Mercedes-Benz E43 AMG 4Matic 3.0L V6
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[@garyvanremortel5218]

Super concise format, well presented. No crappy music to detract from the content. IMO you guys are the Gold Standard for KZbin repair videos.

[@fcpeuro]

We really appreciate that Gary, we are constantly trying to improve our DIY videos and format, glad youre enjoying them.

[@Nohndl]

This has got to be the most thorough and professional service example I have seen. I appreciated details like tools needed, lighting, and even cautionary examples like making sure not to lose parts or damage the interior - even how to keep the frustrating carpet out of the way. Great team job.

[@windsofhealth]

I just replaced mine using this vid as a guide. Took a bit longer than you did but nothing broken and everything looks like it did before the installation. Saved money on service fees and Aux Batt Malfunction message is gone!! Thanks a lot. The video is much appreciated.

[@cforrester2186]

Great to-the-point video! You have saved me the outrageous MB dealer fees to have this done. Bought the part and it only took me 30-45 minutes to do replace on my GLC300 start to finish.

[@fcpeuro]

Great to hear! It is wild what they can charge for a job like this one.

[@tattooedfoodbeast6755]

Perfect video. Easy to follow, and until this video was posted I couldn’t find decent instructions for this super easy swap. Thank you!

[@jamesriley5057]

Agreed. I watched a related video where the guy drops the 8mm screw down in that gap under the rug and turns this simple job into a tedious one real fast.

[@ooguiile]

This was HELLA useful for me and my C63s 👍🏻. Although the aux batt was not burnt, the fuse was blown. So I replaced both and voilà.

[@nathanbryant45]

Thank you so much for a clear & thorough video, was easy to swap the Aux battery with your help. Very professional video 😊

[@sivbum960]

Excellent, the special tools photo of the items needed is a beautiful idea for DIY audience. THANK YOU!

[@joshmills955]

Just done mine. I'm a complete novice with anything like this. Brilliant video! Saved me a fortune thank you.

[@miketoft8168]

Most useful video. Clear and easy to follow. Putting the trim and carpet back was a bit fiddly, but quick and easy even for an amateur like me. It didn't even matter that you've got the steering wheel on the wrong side 😂

[@suzy6005]

Awesome! Good clear instructions well explained. I have a UK GLC 250D (2016) same location and part, plastic a bit fiddly to refit but saved £££ on both the part and fitting so well worth it. Many thanks.

[@johntaylor4057]

Superb presentation. Just the way I like it. Everything described 'A to Z' very well done, many thanks.

[@rockviewvideo8049]

I was a grease monkey rebuilding hot-rods all through high school. However, that was in the '70's and cars nowadays are very daunting with what is perceived as "complicated" electronics. But your videos really make the complicated simple. I completed this replacement in less than 30 minutes and so far, so good. Also, it's one thing to know WHAT to do, but it's another thing alltogether to know that it CAN be done. That was the biggest hurdle for me. Thank You!!!

[@fatboylousa6247]

Thank you very much, I was able to replace it on my E300 without incident thanks to your explanation. No more annoying Aux Batt Maulfuction message... Thanks!!!

[@zuluwarrior791]

Excellent instructional videos, well done Kyle, clear, logical and just the right level of advice and guidance needed for a successful task completion. As said previously these are the Gold Standard for YT MB repair videos.

[@1mpost0r]

Great video, this is how the DIY tutorials should be done! No useless music, list of tools upfront, good angles, straight to the point. Thanks! I have used this video to replace the aux battery on C200 wagon - it was slightly different, but this video gives you more than enough information to get it done. The main differences: - the panel with T15 screw has only single screw and two clips - the footwell panel was held by three nuts - two on the bottom, one on the top left (UK version) - all of the nuts are 10mm (panels and the battery), no need for 8mm The most difficult part of the repair was bending/pulling back the carpet as it was very stiff.

[@fcpeuro]

Thank you for the first hand feedback!

[@mixxedjustright]

This was excellent. Super easy, thanks for walking me through this.

[@whyzeep3778]

Very nice instructions! Great job. Now, I feel comfortable getting started.

[@ssfutube]

Outstanding clear concise presentation. You are the best. Thank you.

[@Harrybollox]

Thanks this worked superbly in my RHD wagon. Only one screw on the first panel, and all three bolts 10mm .

[@Analogkid299]

Excellent tutorial Kyle!! I was a MBZ Factory Trained Master Technician and Trainer back in the ‘80’s and mid-nineties, then moved in another direction and spent 20 more years in MBZ Sales Management. I checked out your video, as my wife’s 2018 C300 just got the “Pull over and leave the car running…” error message. Obviously I haven’t “turned wrenches” in awhile, so that led me to your video. I actually have a MBZ Extended Warranty on the vehicle, so it should be covered under warranty, but I always like to know what’s going on. In any event, being a former MBZ Technician/Trainer myself, I can tell you are a very conscientious and quality technician! You do clean work and your explanations and thoroughness are “top shelf!” I would have no reservations recommending you as a technician! Thanks again for the great video! 👍🏼

[@79jaimes]

Muchas gracias!! me ha ayudado con el problema de la batería de mi coche, dos talleres automotrices no pudieron dar con el problema, y gracias a este video lo pude arreglar yo mismo sin tener conocimientos al respecto. Mil gracias !!

[@simonlefter4824]

Thx to you I was able to changed on my self and save a lot of money! Great job guys keep going!

[@christopherneff7846]

Excellent Video - agree with the other comments - it took me longer to drive to the jobber to get the part than it did to restore the "auxiliary battery malfunction" and test drive. From tools required to the full, concise, logical, and informative presentation. I went back to review removing the wire from the old regulator and aligning the plastic panel that holds the pax light and interior temp sensor and still beat my 40 minute drive time. If you know anything about resetting a 2003 VW European clock spring - I'd love to see a video. Great Job Kyle.

[@user-ns3zy5kb1w]

Job well done. Straight to the point with very much understanding

[@jorgezuniga7777]

Excellent Video & very professional. Now we clear how to replace the aux. battery. Thanks much...

[@chrispiscopo4631]

Thanks very much Kyle. I noticed a couple of small differences with my car which is a right hand drive australian model 2016 c300. The bolt holding my converter was 10mm not 8mm, and I had no second T15 screw holding the upper plastic panel - not missing, just not designed for it. A couple of extra notes to assist with aligning the plastic panels, the upper panel needs to align with an air vent - when I focused on that the panel moved in to place perfectly. Second, the side panel not only has to align with that white arm near the fuse box but also a couple of latches on the side near the door opening. Once I got that the panel sat right against the side.

[@indianboi3]

Thank you so much bro, just got this done on my 2015 C300 W205. Initially the error I had didn't go away but after a couple of drives the error for "shift to P, leave engine running" finally went away 🙏

[@channelwhywhywhy]

Absolutely perfect! Thank you! Just about to replace mine now.

[@arosle2560]

Thank you! I had the capacitor changed 3x times! But the error message was still there. Drove the car for the past 3 years with the error message visible until I saw this. This is the only video that mentioned to check in the fuse in the trunk. And guess what? My fuse were blown this whole time. Bought new 10A fuse and magically error meesage gone! Thank you so much for your help!!!

[@coffeeman2079]

Thank you for this excellent video. The car calling it an Auxiliary Battery threw me initially but after hours of searching found that it was the a Voltage Converter. This lead to your video. Mercedes were going to charge me £150 for a diagnostic (what’s the point of the on board computer telling you exactly what’s wrong🙄) and then whatever the Converter cost and fitting was . Two separate visits and inconvenience not having car. The online search was well worth the time and coffee drinking. Now to get it fitted. You made it look fairly straightforward 👍

[@fizzysausage]

Super helpful, clear and well presented, thank you!!

[@tomwander2804]

First class video. Keep up the great work!

[@osama692110]

Thank you the best auto repair video I have ever seen

[@tyronefinkley9090]

Good job with presentation. Thanks for your help, and God bless you

[@jh9493]

First class instructions!! Just fitted this part to my car 😊 Thanks 👍

[@philandrews9216]

Excellent video, clear,precise but not over complicated. Thanks for sharing. Phil.

[@fcpeuro]

Thank you for watching!

[@melgreen4979]

Great video, really well informed and easy to understand you. I did the replacement in a GLC and it was almost identical. Small problem was the insulation foam cracked quite a bit. Thank you!!!

[@fcpeuro]

Glad it helped!

[@openmind6969]

Will attempt my GLC in next days as well. Any note on what was different?

[@melgreen4979]

@@openmind6969 just the carpet was really awkward to pull back as the side piece wouldn't bend. It actually looked like someone was there before as the foam was broken and I made it a bit worse. But it all went back together ok. Remember fuse 448. Good luck!

[@seyedziaeddinkanani2735]

Great video. Well explained with all the details. Thank you.

[@SwiftHDX]

Excellent tutorial, I'm starting to get annoyed by the error message so after watching your video I was confident enough to order the part and I will be doing the replacement myself. Easily saves me a few hundred bucks. Thank you.

[@fcpeuro]

You got this!

[@kaneda4102]

Legend- you just saved me hundreds by following this. Thank you for this excellent video.

[@fcpeuro]

Nice work!

[@TheLithGH]

Thank you sir! Need to do this, so appreciate your time!

[@ameenerr]

Thank you! This was a great tutorial and very informative

[@umchpetrol]

What a concise accurate video. Thanks very much!

[@ksauto1]

thanks for the great video, found this just in time as I have customer coming in next week to have this replaced. I did notice you DID NOT fully clip the underdash panel back together-one of the 2 clips was not pushed back in on the left side!

[@shaileshakhouri5385]

This helped me save dealership fee. Awesome instructions for each step. Thanks

[@fcpeuro]

Great to hear!

[@matthewbrown33]

You're the man Kyle - very good video ;)

[@Transient901]

Good professional video... Great Work!

[@Doctorj63]

Very good video. Also a great time to replace your cabin air filter.

[@bohjeresen]

Thank you very much for an informative and clear video instruction, I have just completed the task and I was grateful that I could see through all the processes in the task. 😃

[@markerwin2672]

Done. I purchased the part online and took my laptop in my C300. You walked me through every step. Well done! You saved me a ton of money. BTW, The nut retaining the Aux. was a 10mm, not an 8mm.

[@fcpeuro]

Love to hear it, thank you for the note!

[@BassGods]

Is this the same location for a 2016 C300?

[@christopheraden4035]

@@BassGods yes!

[@BassGods]

@@christopheraden4035 Thanks! Replaced!

[@AirgunNinja]

Thank you for posting this very helpful video! The only difference in my 2016 c300, the nut for the capacitor is also a 10mm not an 8mm. Everything else was exactly the same. I, too, can tell someone was under the panels. It was missing one T15 screw and the little hook arm under the top panel was ganked. Again, thank you!

[@1940tony]

m

[@pyourpane]

Did this help? I too have a 2016 c300. Same message on the instrument cluster. I’ve had to replace the alternator and battery.

[@BassGods]

I have same car. Is it the same location as the video?

[@Baykid707]

Great video, you're a lifesaver.

[@krupin12]

Dear Sir, thank you for this guide. Just did the replacement in my coupe, 20 min. of work.

[@gagangowda6600]

Hey Aleksander, did u replace it for a c300 coupe 2017 ?

[@krupin12]

@@gagangowda6600 Hi, nope, I did it in 2016 C43 coupé

[@MrEjoeb7]

Where is the MAP sensor located for a Mercedez C300 4MATIC. I been trying to change it and can't seem to find any guidance. could you do a Vido on this? Thank you for your videos. very educational and clear to follow

[@dr.enricobarberis5949]

Congratulation! Easy for you as you show but for me is mission impossible😂😂😂 Many thanks! Enrico

[@johnjiang1732]

Great video, helped me change the unit today.

[@fcpeuro]

Fantastic!

[@bighonchox6698]

THANK YOU SO MUCH YOU GUYS ARE LIFE SAVERS !! I have the same car but a 2017

[@rareyes3604]

Did you have a problem removing the T15 screw? I have a 2017 also....

[@bighonchox6698]

@@rareyes3604 well I haven’t started it yet because I’m going to order the part next week and get the tools that I need to do this myself. I will have one of my friends with me to help me if I need assistance. So I definitely will let you know how it goes next week or in 2 weeks stay tuned.

[@zdenekmasek9643]

Hi, nice video. What type of connector on cable harness side is used? Some number has to be printed on it. Thank you.

[@billmcquitty719]

Very clear instructions. changed out auxiliary battery but warning still on dash. Any ideas.Thanks

[@George-ww9ob]

Great presentation thanks 👍🏼 my start stop feature on my c300 coupe 2017 works once in a while only and i didn’t get any message on the dash most likely its from the auxiliary battery. I have my rear defroster not working it turns on for a second and then turns off automatically, do you think it has something to do with auxiliary battery too? Thanks

[@Missautumnashley]

Omg thank you so much for this vid!!! I did ittttt by myself !!! Well with God and your vid 🙌🏽🙌🏽🙌🏽🙌🏽🙌🏽🙌🏽🙌🏽

[@colinchapman9261]

Excellent well presented informative video,well done.

[@rareyes3604]

Great video - any tips for removing a stripped T15 screw? I tried to remove the first screw under the passenger side and discovered it was stripped.

[@xiome3145]

Hello Kyle, great video, my 2017 C300 use a T 20 torx and no need for the 8 mm, for the floor panel with the 3 nuts size 10 mm i took a piece of plastic put over the end of the socket and that will help for the nut to stay wedged in the socket. Thanks

[@lb2084]

Brilliant video very helpful

[@meko4838]

Thx this video saved me a lot of money

[@MrJwd1956]

Very good video. Thank you.

[@MBAStudios]

Great Video. You saved me a lot of bucks with it 👍

[@jfarinacci0329]

Really good video. thank you.

[@Plattlane70]

Love your channel quick question does the auxiliary battery effect keyless entry at all. I changed all the fuses but keyless entry still not working. Pain using master key to enter in and out of the w205

[@brownsbikingadventures5679]

Hi great video, I have a c220d 2016 but it's not at that location on the video. Any idea where it could be located? Need help plz

[@keithr.santillo4559]

Kyle...Great demo... How do you reset the Warning after changing the parking pole capacitor..

[@yvesnomine2514]

TRES BONNE PRESENTATION J'AI CHANGER LA PIECE TOUT EST OK MERCI BEAUCOUP

[@bassguitarislife3419]

Good video, very informative.

[@georgelabarta9209]

Well explained thank you!

[@salesmanager8377]

great vido: do youknow if it on the Left or right side for RHD ( Australia) drive?

[@akinobu91]

Just got mine done. Thank you so much!

[@fcpeuro]

Fantastic!

[@oscarlara2268]

You’re the MVP!!!

[@joelsweat2007]

Excellent video! Great job explaining everything very knowledgeable!

[@babstankersley896]

Great video. thanks so much

[@dadart2028]

great video man.

[@TwinSted666]

Great video and exactly to the point!Yesterday i've got the message on my dashboard saying that with red text "auxiliary battery malfunction" then after 1 min the message just appeared on white. Today i changed my aux battery and the message still appears with white then i've check on the trunk and find also my fuse 10N was burnt out. After i changed the fuse the message disappeared. Regarding this i have two questions..is there any chance to get the message about aux battery just because the fuse failed? Also when i changed the fuse it was 10N but i couldn't find the same one so i've got just a fuse 10 standard i belive it is. It's there any problem because it's not the same like 10N?

[@davidarocho9575]

Hi i have a 2018 mercedes-benz C300 2.0l and i change the auxilary battery and the stop vehicle leave engine running is still on i check the fuses and they all good .can you help me out

[@certifiedfresh]

Amazing brother

[@benzeeto7479]

Do you happen to know where the auxiliary battery is on the 2013 e550 Mercedes coupe

[@sebastianbach1761]

I replaced A2059053414 with A2054400073 and everything worked perfect. Are there any incompatibility problems due to the fact that I replaced the newest version by an older one?

[@marsfire79]

Perfect video! Thank you so so much

[@fcpeuro]

Glad you enjoyed it!

[@btyme12]

i have 2009 ml350 when replacing aux battery do you have to reset anything

[@Alex-dk9hu]

Can you provide a link where this part can be ordered at FCP Euro? Thankyou this video was very helpful.

[@yawnerddn]

This video was really helpful and gave me the confidence to perform this task myself. I would have appreciated slightly more detail on how to disconnect the actual 3 pin connector on the voltage converter. I struggled with that until ringing a mechanic friend for advice ! 🤣

[@fcpeuro]

Glad, to be of some help, thank you for the note!

[@michaeldelsignore6980]

He is a very good! Thank you

[@shaygavrieloff7850]

Thank you for your video you helped me to save $400

[@kumantm3241]

Hi sir my auto start stop does not function when I turn on the aircon snd when I turn off the aircon it gunctions again. And the aircon over the time getting warmer and warmer. Is this relate yo aux battery even though aux batt malfunction never activated.

[@kevinpattersonkevin3744]

I changed my main battery and regulator in a 2018 c 180 and still getting the low battery signal if i dont drive it drains with in 2-3 days

[@blagoykolev8129]

Thank you.Perfect video

[@fcpeuro]

Glad it helped!

[@twinpyramidshoney543]

I have the hybrid model but cannot seem to find the auxiliary battery. Where can one find it? 2017 c350e thank you a ton

[@albania3339]

Hi there ive just changed mine today and still comes up with the same message do you think the fuse is burned out? Thankyou

[@abesolano7744]

great video!! ordered the part from the dealership and did it myself before watching this video.. only problem was after it was installed, I am still getting the error code. this video exactly showed me what I missed which was checking the fuze box.. if I fix the fuze would that solve the error messages still?

[@user-sx5su5bw8r]

Thank you. Very helpful.

[@fcpeuro]

You're welcome!