How the heck to use an MB C300 to jump start another car?

Everything else
#1

Hi all, I know this is one crazy arcane question, but here goes. I need to jump start a vehicle but upon opening the hood of my leased MB C300 sedan, I discovered that most of the stuff, including the battery proper, is under one plastic panel or the other (which I’m loath to move because it is a lease). The only easy access is to the positive port, as if to discourage using the Mercedes’ battery to “donate” a charge to another vehicle, because the way I learned it, you have to attach the red clips to the positive terminals on both vehicles’ batteries, then attach the black clip on one end to the negative terminal of the donor vehicle’s battery, and the other one to a metal engine part of the “jumpee” vehicle.

If anyone can steer me to a way to do this I’d appreciate it. Maybe you don’t have a C300 but another similarly afflicted vehicle and I’m just missing something obvious.

#2

Whatever you do, wear eye protection.

#3

Call the leasing company and explain the situation. End with, “And since you made it impossible for me to do it, you need to do it for me at no charge.”

#4

I can answer this because I have this car! The negative clamp goes on a metal pole beside the battey that is attached to the metal car frame. This provides your other pole. Should be right by the battery. If you have any problems locating it let me know and I"ll take a pic.

Edit:. it should look similar to this, design changes for a newer model may have moved the location slightly:

I am actually unsure if I have jumped another vehicle this way. I have definately jumped mine.

#5

Yeah the black/negative terminal should be connected to the vehicle body as ground. Usually it’s right there by the battery if you follow the cable. So you should be able to connect to the frame instead of the negative terminal. In fact this is how it’s supposed to be done on the car getting jumped. I’m looking now to see if the car doing the jumping can use the frame.

Reference for weak battery use frame:

#6

Yeah confirmed: https://mechanics.stackexchange.com/questions/74654/when-jump-starting-a-car-can-i-attach-the-negative-cable-for-the-car-with-the-d#:~:text=You%20can%20make%20either%20or,frame%20instead%20of%20the%20battery.

#7

Thanks, Guap-- what model year is yours? Mine’s a 2020 (we get a good deal through work–I work for a Daimler company) and there are all these thick plastic panels covering most everything. Is what you’re showing there (the copper-colored thing which is what I assume you clamp to) under the hood?

#8

Thanks. One of those replies says you don’t have to access the donor battery’s negative pole directly.

You guys’ Google-fu is way stronger than mine.

#9

Well I already knew that little tidbit and so I was just googling for a reference.

#10

Yes, under the hood, somewhere on the metal bits.

#11

Yeah, no plastic, no paint, no trim. Should be placed on a structural piece of bare metal. Looks like they very considerately put a nice copper lug to tie you into the frame.

It’s almost certainly in the manual.

#12

This is why I have one of those batteries with jumper cables. You only have to mess with one car at a time, less chance for something silly to happen.

#13

Yeah, I knew that you should connect to bare metal with the black clamp, but what I didn’t know was that you didn’t have to use the donor battery’s negative pole. I thought that was a sine qua non. As to whether it’s in the manual, there’s probably some mention of getting a jump, but I’d bet there’s no mention of giving one. Also nowadays the manual is something you have to read on the car’s media screen, which is kind of a pain. The printed documentation is pretty sparse with newer cars, even luxury ones.

And @espressojim I didn’t even know that those were a thing. They come with the jumper cables pre-attached or something? I’m guessing the vehicle is an SUV or Jeep of some kind, right?

#14

It’s a little battery pack and you plug in the jumper cables. Do that, turn the car over, disconnect the cables from the car then the pack, put the pack back in your car somewhere. They are quite small, quite cheap, and usually have a built in flashlight, USB charging, etc for ~ $100.

For whatever reason, I’m a bit nervous about jumping cars from car to car (plus you gotta find another car to help you out) but this sucker you just whip out, plug in, and you’re jumped in 2 minutes.

#15

Yeah definitely recommend those things. I’ve seen them a lot cheaper than $100 too, especially around holiday and prime days

#16

You can even get the jumper packs that have a compressor for tire inflation too. I have one of those.

#17

Oh, something like this, then?

https://www.amazon.com/Weego-Cranking-Resistant-Designed-Engineered/dp/B01MSAXF03/ref=sr_1_2?dchild=1&keywords=weego&qid=1613692794&sr=8-2

That sure sounds a lot easier than possibly messing up my leased Merc’s electronics. I’ve jumped started cars before but I get your unease. It’s not something I do every day.

#18

You can always use the car body instead of the negative terminal, because the car body is always grounded to the negative terminal for safety reasons.

What you’re supposed to avoid is using the negative terminal (instead of the car body) on the receiving battery. That’s the final connection, and may cause a spark while completing the circuit. Sometimes dead batteries leak volatile fumes, and so you want to avoid causing sparks near a dead battery.

#19

Sure, and much less than $100, too.

I have the runner up on wirecutter, and it’s served me well across many jumps of my and my neighbor’s cars.

#20

I ended up ordering one of those and it’s on the way. Very cool.