M_Austin

Hi All;
Considering a new W213 "All Terrain" wagon and have a question.... In the past, I've sometimes had to park my vehicles for several months when traveling (when we all could). I always kept them on a battery tender in a garage. Kept the batteries in everything happy! Now, with the new W213 with a 3.0, it has a dual voltage system, from what I gather. A 12V for all the auxiliary stuff, and a 48V that I assume actually starts the vehicle. If I have to put this thing in lay-up mode for several months, and use my traditional 12V batter tender hooked to the jump lugs under the hood, does any of that "trickle" make it's way into keeping the 48V system charged or am I simply keeping the 12V system happy (another words, I'd have lights and radio, but no juice to spin the engine over)? On another more obscure possibility, what about jump starting these things? In glancing over the owners manual it seems one would again use the 12V jump lugs so I am assuming there must be some kind of step-up voltage happening somewhere in the system to get juice to the 48V side that actually spins the engine over? Did a search, can't seem to find anything....

nycebo

Great question. I'm curious as well. I'll search around and report back if anything appears to address your concerns...and mine.

2012 merc amg

I thought of that too, I think I mentioned it in post about I thinking of getting one of the all terrains, but did have concerns about storing the car. I do not believe the 48 volt battery would charge off the 12 volt battery maintainer. But I don't think it would be a problem leaving the 48 volt battery in the charged state it was left in as long as the car was stored no more than a half year or so. At least thats my take knowing Lithium batteries as I do. They seem to hold their charge fairly well when left with only a 1 to 3 percent discharge rate and I don't believe leaving them not in use will damage them.

JTK44

It is not only the All Terrains but all inline 6 cylinders, for example the E450 Sedan.

2012 merc amg

True thats why I was surprised when I did a search I could not seem to find out much about it. What would really worry me is that in Florida my garage gets up to 120 degrees and it's heat that really kills batteries, especially batteries that are not hooked up to a maintainer.

e55phil

Great Question,

ua549

There are several 48v battery maintainers for sale. Unfortunately most are for lead acid golf cart batteries. The lithium maintainers are just starting to become available ($$$).

M_Austin

Well... I MAY have answered my own question! I downloaded the owners manual for the '21 "All Terrain". Buried in the back... WAY back... are two somewhat obscure references. On page 406: "Connect a suitable charger approved for Mercedes-Benz with sufficient charge output to the jump-start connection
point of the 12 V battery (/ page 311). The 48 V battery is charged via the voltage converter in the vehicle." A similar reference to jump starting the vehicle on page 311 also seems to state something along the lines of connecting the jump leads to the 12V lugs and waiting for a few minutes for the voltage converter to juice up the 48V system, then start the car. So it would APPEAR that a 12V Battery Tender could be used during storage (of course the manual states to use an "approved" MB charger, which really looks like a regular, rebranded C-TEK unit and is 12V) and it indeed will dump juice via the "voltage converter" into the 48V battery. Can't imagine it a very efficient way to juice the 48V system going through some kind of step-up transformer or something, but it appears that's how its done.

ua549

48v lithium batteries are very, very expensive. MB wouldn't want someone to ruin the 48v battery by using an inappropriate charger then make a warranty claim.

The 48v battery is normally charged directly by the 48v starter/generator.

JTK44

I think you are very, very overly cautious. Mercedes would have you believe that when you change your oil you should only use their oil when we all know it is Mobil 1. Ditto when you replace a battery - you should pay several hundred dollars more because on the outside it says "Mercedes".

Ctek makes the banded name charges for many cars, Porsche and Mercedes included. You can buy a Ctek charger or pay double for the same charger that has "Mercedes" printed on the outside.

As M_Austin correctly points out in post #8 the battery charger charges the 12 Volt batter which in turn keeps the 48 volt lithium battery charged.

A Ctek charger will do just fine!

.

ua549

You missed my point of MB not wanting direct 48v charging so that is why they charge the 48v battery from the 12v battery. One can easily ruin a lithium battery or any battery by improper charging. AFAIK Ctek does not make a 48 volt charger for lithium batteries nor does MB market one.

I've owned a Ctek charger along side of my favorite Battery Tender charger for 20 years.

JTK44

I do not think so. Apparently you are confused: this thread is about using a 12 volt battery charger, for example a Ctek and whether or not will it charge the 48 volt lithium battery or only the 12 volt battery.

As per post #8 a Ctek battery charger will charge the 12 volt battery and that 12 volt battery will maintain the 48 volt battery as well.

No one has suggested using a charger to charge the 48 volt battery - nor as post #8 points out is there any need to: a 12 volt Ctek battery charger will do both!

M_Austin

I think several people are correct on divergent points. It seems like the 48V side lives in a separate, sealed universe. There is no way to charge the 48V side directly, it either gets done with the engine running (via it's high output alternator/motor thing) OR gets fed through the 12V side during a trickle charge or jump start event. In the cases of the later, there is referenced a on board voltage converter that takes 12V and charges the 48V side. ua594 is correct; Lithium batteries are finicky about being charged, hence I suspect MB specified and fitted the on board voltage converter to sort out that end of things. With regards to a 12V charger... well... for the most part they are pretty generic and all put out no more than 2-3 amps (max, a lot less in float or maintenance mode) which is easily handled by a conventional 12V battery. And that battery probably acts as some kind of buffer in conjunction with the on board voltage converter to help keep both systems happy. At the end of the day, we only have access into the 12V universe of the car via the jump lugs; so the 48V side kind of sorts itself out if you keep the 12V side happy, in very brief terms. Really wish there was a technical paper out there with an overview of the electrical systems. Would love to learn more. Having almost lost my mind getting my old 1974 MGB to charge correctly I can only barely begin to fathom the tech deployed in these new MB's. Really quite remarkable. NOW... If I am wrong on any of my assumption here, please feel free to correct me! I am piecing these together from what is available in the owners manual, MB's published stuff on-line, and some informal discussion with a MB Tech. But the short version answering my original question would appear to hook a 12V batter tender (or similar device regardless of manufacture) to the jump lugs during lay-up as one would a "normal" car and carry on!

Hundens

WADR, I don't read post #8 to address the issue specifically. I don't have a MY 21 Owners Manual, but I would want to see something in writing, signed, and sworn to by MBUSA that hooking up a 12 V battery manager will work for a vehicle with a auxiliary 48 V system going into storage for an extended period. Jump starting and storage are not the same thing. I recall there were Teslas whose batteries bricked when they were left in storage.

Also, I had a CTEK charger fail on a vehicle. The consequence was buying a new 12 V battery. I hate to think what the cost would have been with a lithium 48 V battery.

Further, Weather Tech and Costco sell a battery manager not from Ctek, but sourced in China.

Still, I expect we will see a lot more on this issue. I would not put an EV in storage with what I know now, and I am not aware of this issue being addressed.

JTK44

As there is no readily way to charge the 48 volt battery all we are left with is charging the 12 volt battery by the readily available positive and negative posts.

That to me is the simple and complete answer. Let's not try to "fix" something that is not broken - how to charge independently the 48 volt battery. By charging the 12 volt with a high quality Ctek charger you will also maintain the 48 volt battery.

JTK44

WADR I think post #8 does specifically answer the question: the battery charger, charges the 12 volt battery which maintains the 48 volt battery.

Good luck getting Mercedes to put:

.

Hundens

44,

"So it would APPEAR that a 12V Battery Tender could be used during storage" Emphasis in original.

"APPEAR" would not be good enough for me. As to getting something that you can rely on, I expect getting anything in writing out of MBUSA is impossible. So you play their game. You send them a letter saying "your guy told me and I am relying on it."

ua549

I was simply positing why MB conjured up a complex inefficient system to maintain a 48v battery via a 12v system. Upon reflection I wonder what the power losses are by converting 120/240 volt AC current to 12 volt DC current then converting that to 48 volt DC current. IMO it is greater than 20%.

2012 merc amg

I'm willing to bet if you put a charger on the 12 volt battery and then put a voltmeter on the 48 volt battery you would see NADA. I'm willing to bet the 48 volt just sits there when the 12 volt battery is charged. I don't think it's such a bad thing though as the losses of charge on a lithium battery really are not all that great and it would probably be well over a year before the 48 volt lithium battery did not have enough charge in it as long as it was fully charged by the car when the car was stored.

JTK44

For all of us who are somewhat skeptical, when you get something in writing from MBUSA, please post it.

I for one, am not holding my breath!

Hundens

Interesting conjecture, BUT what about the Teslas that bricked out after being in storage. I am aware of more than a few people who put cars in storage for the better part of 6 months which is my recollection of how long the bricked Teslas were layed up. Who knows what is going to the 48 V. I don't pretend to know the behavior of a lithium battery. In my ignorance I thought they would need some flow. I know I have to recharge the lithium batteries in my flashlight.

ua549

Lithium batteries do self discharge. IIRC the rate is about 5%. OTOH a modern vehicle never stops using stored energy unless it is specifically put into hibernation mode.

Hundens

Emphasis added.

I expect the constant drain for telemetry and such is why Mercedes Me Connect always says "starter battery partially charged." That is why I lock the car even the the garage, thinking I am minimizing the drain. Is there a hibernation mode on our cars and if so where?

M_Austin

ua549