So, I’m slightly embarrassed to even have to write this post, because the though that the 12 volt battery is probably covered in the 4/50 warranty didn’t even occur to me until after I bought a new one. So recognizing that as my big mistake, I’ll keep going as this might be helpful to someone down the line. Not sure if my battery would have tested as “Bad” to replace under warranty but I should have at least tried.

I was getting the message that the 12 volt battery was critical and to charge or to drive at least 30 minutes (or whatever the app says) message when the car sat for more and more often. Generally, if the car sat for 5 days or so, which it sometimes does, I’d get the message. Since the vehicle is a little over 3 years old, figured the 12V battery was starting to die and I would replace it. Some quick notes for people who have to do this – should have taken some more pictures to help, sorry I did not.



I’ll say up front, this is the hardest battery replacement I’ve done, and a bit of a pain, but most of that was just figuring everything out. Having been through it now once and knowing how to do it -- will be quite a bit quicker the next time. There wasn’t much in the way of videos or stuff to help, although there were a couple where I could at least get a glimpse of what was going on.



First, for the battery itself, the cheapest replacement I found was an AC Delco Gold battery from Summit racing. Was around $180 with free shipping and no core charge. I’ve had excellent luck with the AC Delco Golds in the past. Rock Auto had a battery for slightly more and a $12 core charge. The battery from Mercedes seems to list around $310, but a few places had it for $257. One online Mercedes parts dealer actually had the Mercedes battery for $160 or so, but wanted $175 to ship it, so not a good option. I figured if I had this done at the dealer, I was in for $300 in parts, at least an hour of labor, plus all the misc shop and disposal fees and such that they come up with, figuring at least $500 and probably more like $550-$600, so the $180 out the door DIY method seemed like a better option.



Now for the actual install. The battery is under the driver’s seat in the US (and other LHD countries – should be the passenger seat in right hand drive countries). Unlike other cars with battery under the seats (including pervious generation GLSs) you can’t just slide the seat forward and access. You’ve got to remove a bunch of stuff. Here’s some notes:



· Remove the driver’s seat (has to come all the way off). It’s probably easiest to disconnect the wiring harness, but if you are careful, you can rest the seat on the rear passenger floor and leave the harness connected. Will make getting things out a little more difficult this way, but still doable. Seat is bolted in with 4 of the reverse-torx star bolts. While you are doing the rear, take out the plastic vent under the seat, it snaps right out.

· Remove the front and second row threshold/sill trim pieces. These are in with clips and pop out.

· From here you should be able to roll the front carpet forward so you have access to everything under the seat. There is a plastic panel held on by 4 plastic bolts (think 10 mm) that is the goal– but you’ve got to move a few things first

· There are two foam ducts that connect to the hard plastic ducts coming from the center console. One goes to the B-pillar for the backseat upper vent and the other goes under the seat for the rear passenger floor. One of them is held on by a pop click thing removable with a screw driver and the other just needs to be disconnected by hand from the hard vents.

· The seat wiring harness is attached to the plastic vent by two of those push-screw things. A little effort to wrangle those out. Might be good to replace with new ones as they get buggered while taking them out, but I l re-used.

· Now is a slightly difficult part that I didn’t entirely solve. After you unbolt the 4 bolts holding on the plastic panel, it still can’t come out because it is blocked by the hard ducts in the center console and the B-Pillar. I loosened the B-Pillar vent, because it is relatively easy to do. Take off the lower B-Pillar trim panel and then the vent is held on with a pop screw thing. Mine did not come off very easily and got pretty damaged taking off, but I made it work (and it went back on ok). My mistake here is I left everything half in place, but if you remove the entire B-pillar panel and take the vent completely out, you probably are good to go. I could not figure out exactly how the center ducting was attached to the center console (and not sure I would need to if I totally removed the other one) Getting to it meant taking off more trim around the center console and more carpeting. I didn’t want to deal with this, so I went with the hope that I could wiggle this around enough to get it out from underneath and get the panel out. I think that is doable (probably more so if I entirely removed the B-Pillar panel and vent over there, but since I just popped those loose it was harder). After trying for a bit to get it off the panel was just getting hung on the left front seat mount (it has a lip). I decided that trimming a tiny bit (like 1-2mm) off the plastic at that spot would make my life a lot easier. This panel is under the carpet, so no one will ever see it, and I was rolling with the fact that the extra mm off of a thin piece of plastic wasn’t going to increase and cabin noise a measurable amount, so I did it. After that, everything was easy.

· Once this plastic piece is off, You have good access to the battery. The terminals are 10mm screws and the battery hold down bolt was a 13mm. Thankfully both the old and new batteries had handles making it easy lift out the old and drop down the new.

Reverse everything to put it back together and you are in business.

And that’s the 12 volt battery replacement.

New AC Delco battery and original MB battery. AC Delco has slightly more capacity. Probably same manufacturer as the case is so similar.

Here's the piece of the plastic I trimmed a tiny bit -- otherwise it was hard to get over the lip at the top of the mount. Not needed if you properly remove the ducting -- only for the lazy like me.

 

Thanks for writing this up. I recently replaced the battery in my wife’s Audi A4 which was much easier, as the battery is in the trunk and you only need to remove the spare tire to get to it. But I found after doing the replacement, that the battery needed to be “coded”, which means either buying an electronic tool to do it or taking it in to the dealer to have the software updated for the new battery. I didn’t find this out until after the new battery was already installed. The car started and ran fine without the coding but according to what I read on various forums, without the “coding” the battery would not recharge efficiently and therefore wouldn’t last as long as the original battery (10 years).

My question is, did you run into this on the Mercedes battery? Does it require any software updates?

 

I changed the battery in my 2007 GL450 after a long and arduous process where I even had to buy new tools. Only to have the electronics randomly turn off while driving. The battery needs to be coded so this is not something I would bother with DIY.

 

So, I didn't have any issues and all seems to work fine. I did read that in the previous generations there is an option for tech to reset the battery counter so the system knows the age of the battery and adjusts charging to that. However, plenty of people have replaced batteries without updating that (which doesn't necessarily mean it's a great idea -- the new battery life could be somewhat shortened if it is over charged). I have no idea if that same system is implemented on the X167. My plan is to figure that out, and if need be there are some cheap scan tools that do that procedure (or I can ask the dealer to do it). Even with the scan tool, I'm still cheaper than the dealer. Don't think it is urgent, a few cycles without it isn't going to be impactful, but I'll keep people posted.

 

Good writeup. Nearly the same process as mid-2010s Touareg, Q7 and 958-gen Cayenne. Batt under driver’s seat and seat needs to come off.

 

There was me foolishly thinking it'd be somewhere convenient...

 

I just did this on my 2020 GLS and they seriously made it way too complicated. Took around 4 hours, most of the time due to me figuring out to get all the necessary vent/clips off without them breaking. One thing I want to note is that it is highly recommended you disconnect the battery negative terminal first before you disconnect the wiring harness to the seats. I didn't do that and after I changed the battery, an airbag warning came up on the front left seat. I had to use a semi-decent OBD scanner to clear the code and also to reset the battery on the ECU.

 

Here is a great video with every step from beginning to end for the x167 platform. I used my 2026 LAUNCH Creader Elite for Mercedes-Benz (Amazon) to reset battery afterwards, and it worked perfect.

x167 Battery replacement video