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2016 metris passenger.

No aux battery installed under driver seat and wanting to put a battery there for our 35 liter 12v fridge. I’d like to connect a charger to the van’s main battery for charging while driving.

Question: What is the simplest way to access the power from the main battery? What are the wires under the driver seat and are any of them coming from the main battery that I could connect in to?

Thanks!
 

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Welcome Starr -- I'd start with this thread. Sterling Battery to Battery Charger Install

Don't forget to disconnect the main battery before you disconnect the airbag sensors under the seats.

Also, unless you're super-experienced, I'd buy a factory manual to identify the electrical connection points. I'm attaching the BEG (upfitter body & equipment guideline), which is very useful, and a must if you are serious about safety. You can browse Daimler's upfitter portal here. Daimler Vans Upfitter Portal - Home

RansomRidge used the A2 100 amp connection point for their battery to battery charger power source. See their pic below.

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I have the auxiliary battery so I am using the starter battery side of the E36 relay under the driver's seat to connect my Redarc BCDC1225D (smart alternator) battery to battery charger to a second house battery. The pics below show the E36. You're going to want a relay or B2B charger between the batteries if you add a second battery.
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I'm keeping the 95 Ah AGM auxiliary battery and using a Blue Sea Systems 6008 A/OFF/B switch to select either the factory auxiliary AGM or my house battery. Simple way to buy a few amp hours off the auxiliary battery.

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With new battery cables, I am using a terminal fuse on the auxiliary battery to protect that cabling, which will (cutting in progress!) run out of the driver's seat in 1" liquidtight nonmetallic conduit (needed to handle three - 4 AWG battery cables (auxiliary +, auxiliary -, E36 + to Redarc).

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I am grounding everything back to the auxiliary battery rather than using additional chassis ground points, marine-style. I found that the plastic fascia plate on the rear of the passenger seat pedestal fits on the driver's side as well, so I ordered another one for the driver's side -- only about $25 -- which is cheap for MB plastics. The end result will be a floor-level 1" grey flexible liquidtight nonmetallic conduit coming out of the driver's seat pedestal then turning 90 degrees right to the driver's side. It's a run of about 20 or so inches. My "power center" (house battery, fuses boxes, bus bars, Redarc, Redarc fuses, etc.) will sit between the B and C pillars in the "galley" area behind the swiveling driver's seat. The Redarc gets in and out 40A fuses.

Have fun!
 

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2016 Cargo converted into a camper van
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Startech2000- I have a 2016 cargo so I'm not sure if the wiring under the driver's seat is the same as the passenger model. My van certainly did not have any heavy gauge wire under the driver's seat that would have been suitable for charging a second battery. And its unlikely yours does- why would MB install the wiring harness if there is no need for it?

Securing a battery under the driver's will be a challenge. There isn't much space to work with. It would be very helpful to see a van with a factory installed aux battery. You might be able to get part numbers for the hardware used to secure the battery.

Have you taken out your start battery from under the passenger seat? You'll get a better idea of the challenges by looking at how that battery is installed.

The A2 connection that I used to power my Sterling battery to battery charger has worked perfectly- no problems at all.
 

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My experience trying to access the aux battery under the driver's seat is that the space under there is tighter than a pair of kissing proulahs.
I had a real challenge getting a large enough gauge wire from the aux battery thru the bulkhead to my house battery.
 

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My experience trying to access the aux battery under the driver's seat is that the space under there is tighter than a pair of kissing proulahs.
I had a real challenge getting a large enough gauge wire from the aux battery thru the bulkhead to my house battery.
Don't freakin' say that mo -- You're scaring me because I've only rough-eyed the layout. . . . But it looks doable with the 4 AWG cable I need for the 30" run from my replacement terminals (needed to handle 100A terminal fuse) to the A/Off/B switch. Were you trying to avoid drilling through the seat pedestal? I'm just using 1" conduit.

Anyway, the first pic below is the best I have of my driver's seat auxiliary battery space. On the bottom or floor, there is a raised sheet metal channel that retains the aux battery. I measured enough width between that channel and the interior edge of the seat base to route the battery cable. As you can't really see from the shot, the positive cable actually routes to the rear of the compartment and then to the right to the positive terminal. You can see that better on the second pic where the aux battery is out and rotated 90 degrees clockwise from its installed orientation. What am I missing?

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So, what I found was that the space between the positive terminal and the battery box was extremely tight. I was using 1AWG wire to my inverter and found it just about impossible to fit the battery back. it might have worked if I drilled thru the floor so my cable could have looped down and then back in, but the challenge is that once you get this all together and put the seat back in, you really cannot service the battery any longer w/o removing the seat.

Now, you are running 4AWG so it might be easier, but be aware that any aftermarket treminal clamps that might handle boththe factory and your wire might be too large for the space...
 

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So, what I found was that the space between the positive terminal and the battery box was extremely tight. I was using 1AWG wire to my inverter and found it just about impossible to fit the battery back. it might have worked if I drilled thru the floor so my cable could have looped down and then back in, but the challenge is that once you get this all together and put the seat back in, you really cannot service the battery any longer w/o removing the seat.

Now, you are running 4AWG so it might be easier, but be aware that any aftermarket treminal clamps that might handle boththe factory and your wire might be too large for the space...
Thanks much mo -- that's what I suspected. I may run into trouble with the terminal fuse, but I could relocate (and change) that fuse to the space immediately behind the battery. I'm not going to run an inverter off the aux battery so the 4 AWG should be fine.

So where did you exit your cables?
 

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