Moving battery to trunk, any suggestions?
 

I want to move the battery in my brother's W116 300SD to the trunk. I have already figured out how to route the positive wire, but I need some suggestions of how exactly to do the other parts.

1. What gauge wire should I be using to go from the front of the car to the trunk? I am planning on to put an amp and subwoofer in the trunk to balance out the sound system (bigger alternator is on the way). Would 4awg be fine or should I go for 2awg?

2. What should I ground to? A hitch is bolted to the bottom of the spare tire hole (not technical term), would that be fine to bolt to?

I don't understand. If you aren't racing, you shouldn't have much of a reason to move the battery to the rear. If you are racing, you shouldn't be putting in amps and subwoofers. What's going on?

It frees up a lot of room in the engine bay and helps weight distribution

(And batteries in the trunk are cool)

The bracket for the vent for the battery tray was extremely loose and rusty (ground goes to this bracket, ground was poor) so we removed it, started cleaning it up but its pretty knackered up and needs to be sanded, painted, the bolts for the battery tray drilled out, new nuts welded on, then weld it back in (which will be done eventually. We need the car ready by Saturday and I don't have much time between now and then to do all of that work. I can't weld it, my friend has a welder and the expertise and can't do it until later, and running the wires will be easier.

I also see benefits of moving the battery such as no more battery acid leaking into the engine bay, which killed the window washer pump ($70) and reservoir ($60). The battery will be in a sealed box to make sure there is no acid leaking into the trunk. Supposedly there is extended battery life because there is less heat in the trunk, these batteries are quite expensive so its nice to have them last longer.

90 - 01 R129 SL's and 95 - 00 C class W202 have the bat in trunk, 96 - ? W210 E class have the bat under the rear seat.

I'd have to measure the cable dia but it looks to be AWG " 0 "

On the ground side, run a cable from bat to body. Then run a cable from starter mounting bolt to body. AWG " 2 " should be fine for the ground since it is a short run.

The engine to body cable is critical, if left off other smaller grounds will be overloaded. Sometimes items like speedo cables , shift cables , bearings become a ground path.

It's some kind of disorder I think. :D If you think putting the battery in the trunk is uncalled for, there's someone putting it under the back seat. Sure, it's gonna be unique. Bragging rights!

Instead of moving the battery, put an additional battery in the trunk. Run a 0 gauge wire from the front battery positive to the rear batt positive, and don't forget to put an inline fuse.

You can make your own ground, just find a good chunk of steel and sand it.

You will add an additional 700 or so cranking amps, and the rear battery will act somewhat as a capacitor to your amp.

I might do that later when I can get this bracket back in and have some cash, I would put an AGM battery in the engine bay (Sam's has a Group 49 AGM battery for $165).

Get 20 feet of cable. I know folks say it can be done with less, but not so IMO. Hop on S T D dot com and I did it. Now, I am going for under the back seat. It can be done, but it's pricey. Only benefit that I can see is more space in engine bay, simpler design in some regards but more issues on the other end. Get a quick release from Anderson. It's nice to un-do the battery with a click. When you route the cable through the back, but a jacket over the cable, e.g., plastic tubing or something similar where it runs thru by the fuel tank. Maybe overkill, but at least you'll have peace of mind with any vibration.

What gauge wire did you use?

EDIT: Never mind, I found it. I think I will go with the 0 AWG since I can't get 1 AWG at Lowes. I still may try to fix this bracket because my friend just told me he is open Thursday to work on it, I can get the rest of the work done by then, and its cheaper to weld than spend $40+ for wire and $20+ for a box.

Lowes usually sells home building wire. This is not what you want to use as the thick strands make it difficult to work with. And, home wire is usually aluminum so you need to go up a gauge to equal copper.

Truck parts stores have the wire you want for battery use or you can use welding cable.

I am not sure that is correct. All wire I have purchased for my home (20-50 amp circuits) has been copper. Do they switch over to Aluminum at those really large sizes?

The 2/0 wire has an aluminum option. Nothing they sell at Home Depot Is ok for this application. You want to go to a stereo shop, truck parts house, or welding supply. You want to find 0 gauge copper wire that is the thinnest strand possible.

I've done several of these in race cars. For the S-10 I bought 25' of #2 welding cable from the welding store that I use. I don't remember the price but it wasn't TOO bad.

I got 25' because past experience has shown that it's best to run the ground back up to one of the starter mounting bolts. I know it seems like everything SHOULD ground thru the frame and sometimes does but I've had too many problems with electrical gremlins when I don't do the Big Ground. Also be sure to ground all components together - body to engine, engine to frame, and if you do the extra ground, battery to engine. You want NO resistance anywhere in the ground circuit.

Dan

You can probably pull some parts from a late model W107, the battery for those cars is in the trunk IIRC.

Pelican Technical Article - Mercedes 450SL R107 - Battery Replacement

http://www.pelicanparts.com/techarti...mall/pic04.JPG