Yea just thought about this, forgot how hard even 6awg wire from lowes is to work with. I don't know anywhere local that has wire like that, no welding or truck parts places besides dealerships but there are some stereo shops. I think I am going to upgrade the grounds in all of my cars anyway so not a bad idea to find it even if I don't move the battery

you will get ZERO additional cranking amps... but you will get additional capacity. cranking amps is a function of the battery design, and it is NOT accumulative. what this will give you is longer attempts to crank the car before it dies... better voltage under load, and faster starts, IF the starter was overloading the battery.

94+ v8 Eclass has the battery in the rear also...

I think greazzer did this on his 123, and is also the guy moving his battery to under the seat!
Check his sleeper threads, im pretty sure he included some pics of what he did exactly.

Cant imagine the exercise would be that different for a 116. Definitely post some pics of what you do, i also need to do this on my 114 as well

To clarify, I should have said home wire above # 4 or so is usually aluminum when purchased at a big box home center. Home entrance cable is nearly always aluminum.

You can get copper in larger sizes at a electrical supply house but it still will be thick strand and hard to work.

If you drive the car backwards all the time the battery will have effectively relocated itself to the trunk, of your now rear engine front wheel drive Mercedes. OK now that would be cool, and you could be the first!

Two batteries in parallel will give more cranking amps, the affect is the same as a physically larger battery.

If a battery has a poor Peukert number is won't like rapid discharge ( cranking ) but will do better over a long draw. Still, it would have to be impossibly bad for a a pair zero gain in cranking amps.

Great thread! What a novel idea, relocating the battery to the trunk!

Please, please don't move the battery to under the rear seat. If you must, make sure it has the proper vents on the battery and car to get the generated gases out side the car. If the gas builds up around the battery, then you get an arch from a bad connection anywhere around the battery, you could get a very violent explosion. I have seen this happen in a Buick and it wasn't nice. If anyone had been sitting in the seat, they would have been hurt/burned very badly. It happened when the driver tried to restart the car after being run for a long time. He had stopped to get fuel. He only received a bad head ache and was very lucky. Car was totaled.
The same thing could happen with the battery in the trunk. Now remember where the fuel tank is in a Mercedes.
Venting of the battery is the important part here. Some batterys have the proper vent hose connections and can be used safely.

Next safety issue is in using 2 batterys, one in the front, and one in the rear. Please put large notes on the batterys saying that there are 2 batterys. Why? If someone goes to work on the car, say the starter or alternator and they unhook the front battery but the rear (unknown) battery is still hooked up, it could cause them great harm.

Please don't dismiss the above and say "Oh, that can't happen." I worked on electrical problem for 28 years professionally and have seen both of the problem happen on more than one occasion.

Paul

If the explosion danger don't harm you quickly, breathing the fumes will harm you slowly in a not properly vented system. It's one thing if done by car manufacturers where stringent safety requirements must be met. Not a good idea unless it's a race car

Before the alarm bell is rang regarding the potential fire ball of death ... take a peek at some newer technology batteries. Relocation under the back seat, for example, involves NO lead acid batteries. They DO NOT fit. They are too big. EarthX, et cet., and the newer technlogy batteries are non-toxic, they don't ooze toxic fumes, or any other of the nasty stuff which LEAD ACID batteries do. Actually, they can be mounted or oriented in any direction, even upside down (some of them, but not all manufactureres).

In regards to a trunk mounted battery, there is ample room on the passenger side rear cargo "pocket" area (or the driver side too). There is NO need to lose your spare tire. No one mentioned this, but the spare tire in a W123 is actually part of the safety features for a rear end collision. The only confusion about a trunk mounted battery is a forum member who claimed and jumped up and down it won't fit. Well, a Group 49 Battery does in fact fit. I had a battery box oversized to permit dense foam all the way around. and it still fit perfectly in the cargo pocket area.

As for all of the anticipated problems, I discovered nor had any of them.

Battery Box Relocation

I had the battery in my trunk, neatly and nicely tucked away in a homemade battery box for well over an entire year. As for charging, no issues. I ran a bunch of electrical odds and ends for my WVO system and still kept the OEM 55 AMP altenator and never a charging problem, never a starting problem, et cet. My car got totaled and that ended that until I got a new MB. The only thing I would do different is the following:

1. Thicker cable, next size up
2. Make sure you try out some Anderson connectors
3. Get 20' feet of cable and don't sweat being short
3. Think about under the back seat. Very pricey compared to a lead battery, but it neatens up the area. I initially said no way, but I was 100% wrong on that. I had to search outside of traditional batteris. The folks at Odyssey, EarthX, and a few others really know batteries, their safety issues and considerations, et cet.

Does this mod HAVE to be done ? Of course not. It's not necessary at all. But, if you are doing mod's which require turf be cleared out, then it's an option.

Also moving the battery to the trunk would make it much less of a pain to take out from the bay, which takes much fidgeting and annoyingness.

I would do the same if there werent giant puddles of water forming in my trunk after it rains.

Yes, access is simpler and more easier. Just like moving the oil filter housing ... easier for clumbsy folks like me ! :)

It's not a new idea. For drag racing in the sixties we used a marine battery box and mounted it as far to the right rear as possible to help traction. We used cable
Barely he y enough so as to save weight. For street purposes however, use HEAVY cable
For such a long run. No lighter than 0 I would think.

you old Greazzers ... :D