Am preparing to replace the main battery in my 2014 ML350. Do I need to maintain power (via a jump battery and the under-hood jump points) while the main battery is disconnected? I'd prefer to not have to reset the roof, windows, radio, etc.

Of late I usually provide supplemental power when replacing batteries but this car has me nervous that the positive terminal might touch the body or some other grounded metal when I'm pulling the battery out from under the passenger seat. I don't want to cause a short.

Thanks

 

Curious about this as well.

 

Nobody replied to my question about whether maintaining power is required or not so I decided I would maintain power unless I felt that it was likely that the positive terminal would touch metal. As it turns out the positive terminal is on a very short lead and doesn't move much from it's normal position. You can push it a bit to the right to get it out of the way without risking touching metal. Of course, as you reach in there with your socket extension to loosen the positive clamp, take care not to let your ratchet handle touch anything metal.

Maintaining power: connect a jumper box or a spare 12V battery to the car using the jump points under the hood. Slide the little red door up and the positive jump peg is accessible. If your jumper box has the typical little clamps then they'll fit into the positive jump peg box. I was using some heavy-duty jumper cables and could only get one jaw of the clamp into the box. But it still made a good connection. The negative jump peg is exposed and is about 1 foot toward the front of the car from the positive peg.

I followed the rest of the instructions for the battery change: lifted off the cover, cut the carpet (more on this in minute), removed the pop-lock (and lost the center lock-pin) on the air deflector and removed the deflector, removed the access cover, removed the vent hose, removed the holding clamp, removed the negative terminal and pushed it to the side, removed the red plastic grounding-protection cap from the positive terminal, removed the positive terminal and pushed it to the side (just a little), and wrestled the very heavy battery out.

Installation of the new battery is basically the reverse of the steps above.

Some notes:
- your new battery has vent ports on both ends. Remember to put a plug into the one on the positive terminal end. Your new battery should have come with a couple of plugs. If not, pry the one out of the old battery and re-use it.
- remember to connect the vent hose
- your new battery will come with a plastic grounding-protection plate for the positive terminal. My OEM plate from the old battery seemed a little thicker and fit the new battery perfectly so I re-used it. No biggy either way.
- wear gloves when wrestling the old battery out and angling the new one in. The batteries are very heavy and you are in an awkward position behind the passenger seat. I scraped up a knuckle or two because I wasn't wearing gloves.
- try not to pull the center pin all the way out of the pop-lock that holds down the air deflector. No big deal if you do - you can put it back in. But I lost mine. The now pinless pop-lock still works to hold the air deflector in place. I've got some pop-locks around here somewhere - when I stumble on them I might replace the deficient one. You can buy pop-locks at any auto store.

Cutting the carpet: the carpet is "baggy" and I've seen some posts stating you can do this change without cutting the carpet. I believe you could but it'd be a lot more wrestling - a second set of hands might make it easier. But I just made two 3-inch incisions in the carpet as the MB instructions suggest.

 

The "MB instructions". Does anyone have these handy as a PDF file?

 

See attached 'Battery removal.pdf'

 

Perhaps MB made battery replacement trickier than it should be but the job is doable provided you can work from your knees while leaning in from the passenger-side rear door. But be aware - you'll be in a less-than-optimal position for handling the 60 lb battery. It's one thing to pick it up from a shop bench using both handles equally - it's another thing when you are on your knees, arms forward and away from your body, with one hand in front of the other.

 

My 2014 E-class remember everything with battery disconnected, even garage codes, when I did not try it with GLE yet.
Adding battery jumper when removing battery is a risk of sparks, shorts and resulting computer frying.

 

Your experience with your E-class may or may not apply. I'm hoping to get a reply from someone who knows with certainty.

I've read W166 threads saying if the battery is disconnected, the car will need some resets including retraining the windows, steering, and possibly the sunroof. None of those are big deals - instructions are readily available online. However, some threads mentioned needing to go the dealer to reactivate the radio, a headache I didn't want.

I too would find it preferable to eliminate the shorting risk (i.e. not maintain power) but a great many cars do require constant power even during battery change. It would be good to know with confidence if the ML350/GLE does or does not require un-interrupted power. And the second question is: if it does require power and none is supplied, can all the resets be completed in the driveway?

 

I agree esp. a vehicle on can-bus
What about the aux battery. I thought the Aux battery is the backup battery if anything happen to the main battery.

 

There are many videos including specifically for the W166 that show the power being maintained. There are many devices available specifically for this purpose though I used a regular car battery and jumper cables. The first thing that many battery shops do before changing a better is plug in a power maintainer.

Many batteries are under the hood and the risk of shorting the positive terminal is slim. I changed the battery on another car where the instructions specifically required power to be maintained - however that car's positive terminal was encased in a little plastic box that you open to loosen the clamp then close again when you lift the terminal off.

The quandary on the W166 is that there is no such plastic protection around the positive terminal and there is metal in the battery compartment. As I said earlier in this thread though, the positive lead is very short and there is no way it can drop to the bottom of the compartment or reach the exposed metal on the other side.

So let me re-phrase my original request: Does anyone know, with certainty, the MB recommendation about maintaining power in W166 when changing the battery?
The followup question is: What happens if power is not maintained?

The little backup battery in the right side inner fender supplies power to the electronic shifter. It does not supply power to the rest of the car.

 

Even when I drove older MB models, who require wheel sensor reset and all openings calibration, I did not risk jumping the system.
Only radio code took about a minute to find and enter, wheels sensors took 10 seconds to reset, when window and roof calibrations could be done while driving.
As you noted- even if you'd need it on GLE (what I doubt) - not a big deal.
Modern command centers are VIN coded and that stays even with power disconnected.
It is shorting the system who can lock the radio.
MB USA was always offering radio code finding and reset for no charge, so I hope they do it with new technology as well. Just in case you need it.
Audi dealer wanted $120 for code finding 10 years ago.

 

A masterpiece of German engineering. To change the battery is a nightmare. I started to miss my Hondas when it comes to maintenance. I think German should hire Japanese engineers for technology, they can work on the engine blocks and leave electronics and infrastructure designed to the Japanese.

 

sub76sub,

I think some of it comes from trying to balance the car. These group 49 batteries are big and heavy. Putting it low and under the passenger seat makes some sense in this regard. Many Audis have a similar size battery placed below the spare tire.

But consumable items should be easy to replace and this W166 battery change is a bit of a hassle. And requiring the carpet to be cut is absurd. It appears that the auxiliary battery in the rear fender also takes some dexterity to replace (am going to do this job soon). However, both jobs can be accomplished, especially if you understand the steps to take.

 

kajtek1,

I believe the radio code is on a little card included with the original manuals. But if you don't have that your options are:
1) be at the mercy of a dealer to provide the code to you
2) remove the radio and see if there is a serial number decal on it

I agree that resetting the steering sensor by turning the wheel lock-to-lock a few times, and retraining the windows and sunroof only takes a minute or two. Does anyone know with certainty if there's a risk of the radio requiring a reset on a W166 if the battery is disconnected?

Your experience with your 2014 E-Class suggests that things are likely to go smoothly even if disconnecting the battery. But I'd like to hear from someone with specific W166 knowledge or experience. It seems several readers are interested in learning this.

 

Hmm, I used to have E class and they used trunk for the battery which is very easy to access. Yea that is funny to cut a carpet to change the battery, it looks like they don't trust their customer so they used this process so that they know if it is cut then it means the battery is changed which will then void the warranty of the new battery ( Thinking loud). Looks like they successfully did a good job in hiding and making it difficult to change the batteries. A Japanese eng and a common person will consider putting both batteries in easily accessible areas like the trunk or in the engine compartment. It is like this getting bread from Costo and eggs from circle K ( One battery at North and the other at South location..lol)To be honest I do not feel comfortable with anything that can cause a spark below the seats anyway. If there is a noble prize for hiding batteries then German Engineers of MB and BMW should get it. Just my thoughts about MB engineres.

 

The 2nd picture is correct - you need to make two cuts about 3-inches in length. But the 3rd pic and caption about folding the carpet toward the BACK of the car and moving the passenger seat to its rearmost position make no sense.

I put the passenger seat into its highest and most forward position before I started and never moved it again. After making the carpet cuts I folded the new "flap" forward to give me access to the entire battery compartment. The rest of the job is as per instructions.

 

You guys are splitting the hair about the job.
On W210 battery was under rear sear, where releasing seat locks took some research.
On Sprinters battery is under driver feet and you have to remove all vinyl flooring before you reach the battery cover.
It is all not a big deal once you figure it out and takes a minute or 2 to remove.
For me lifting 80 lb battery over the the fender in W212 is the harder part.

 

Honda was one of the more complicated cars to maintain. In fact, it was so complex that it hurt their sales. Along with premature engine and transmission failures.
Their answer? An Ad campaign that said "Honda, We Make It Simple." It was everywhere - a Media Blitz. is one that talks about their key, diverting attention from the real complexities.
And then one of my all-time favorite ads with the tag line "Isn't it nice, when things just work?" Effectively overcoming their weaknesses.
And it worked. Many people still think they are simple to work on, except the shops who do the work. There are a whole bunch of them, since home mechanics find it difficult to do routine work.
Media Reigns and shapes our perceptions.

 

Does the dealer cut the carpet when replacing W166 battery?

 

Connects to your OBD port. You’ll find it described and demonstrated in this video by a well known Mercedes tech up in my neck of the woods.


I have an OBD to lighter socket version of the tool, which is even handier to use.

 

YES. That is the procedure. There is no other way of getting to the battery and is how WIS states it need to be done. One needs to understand that there are "lines" already in the carpet indicating where it need to be cut (only two rather short parallel cuts front to back).

 

thanks threeMBs

 

I have not yet replaced the factory battery from my GLE but the GL63 did not need the carpet to be cut. My X164 GL450 did need to be cut.

 

There B motors were like Lego's I use to build Frankenstein set up mirroring LS bottom end with B16 heads all the time but I do agree on the Automatic transmission failures that's why it's better to get the manual trans.

Now I see the K motors swap all the time.

 

I do not know about X166/X164 (I have/had three W166s, however from what I've read the procedure should be identical for X166/X164), but if one buys used W166 ML/GLE AND if carpet does not need to be cut this means that carpet was ALREDY cut by previous owner or dealer and battery was already replaced or was worked on. There is no other way around it for W166 (and I assume for X166 as well). Period.