Adding a Second Battery? - PeachParts Mercedes-Benz Forum

pawoSD · #1 03-20-2005, 11:22 PM

I noticed a couple months ago when I was at the auto-show here in Grand Rapids, that all of the bigger diesel vehicles on Display had DUAL 100amp batteries in them, such as the Dodge Cummins Pickup, the Chevy DuraMax, the Ford Powerstroke.....and such. They all had two 100amp batteries up front in the engine compartment, from what I could tell by inspecting it, is that they were rigged in parallel, to produce the normal 12.5-13 volts, but with twice the amps. I've heard powerstrokes and Cummins trucks start up, and their starters sound insanely powerful

I've always wondered what advantage it would give on a car such as mine, with a 617, to have a parallel battery setup like that, as it gets real cold here, and in the fall I'll be going up to the edge of canada for school, and I'm still going to need my car, but the chances of having an outlet for the block heater at school are pretty slim, so I was thinking that if I set up a dual battery system like that it'd give me a lot more juice on startup, the glow plugs would get hotter since two batteries would be sharing the load, and the starter would have a whole lot more amps to work with allowing it to crank faster and longer. Mainly I'd like to make the chances of not being able to start it in those conditions very low or non existant. I'll be doing a valve adjustment and stuff before I go there, but I need it to start in temps probably as low on occassion as -10, maybe lower, I hope not. So what boost would a dual/parrallel battery system give?

1985 300SD Sady · #2 03-20-2005, 11:58 PM

First off, I think that you mean 1000 amp batteries in those cummins you speak of...

They sell kits you can buy to rig up a two battery system, last ones I saw were on the JCwhitney website.

pawoSD · #3 03-21-2005, 12:08 AM

Yeah thats what I meant, the "1000 cranking amp" ones. My MB OEM battery that died in December just said "100 amp" on it. My new Diehard says 1000 cranking amps. What I wonder is though, how much advantage would it give to have the dual setup, I'm thinking it'd be quite beneficial since quite often when its that cold my battery holds out alllmost long enough to get it going, but then it reaches the point where its coughing and starting to fire, but then it slows down and looses it when the battery gives out, with two it'd keep it up and get going.

turbodiesel · #4 03-21-2005, 12:35 AM

Wouldn't give any advantage.. if you have problems starting your car, you need to find the source of those problems (glow plugs, starter, compression, etc). Mercedes designed the electrical system to work perfectly starting the car.

The trucks have two batteries for a reason, it takes ALOT of energy to fire the glow plugs and spin that much bigger diesel engine over in sub zero temperatures to get it running. Also, these trucks were designed for towing, and alot of trailers have electric brakes and alot of lights. As a side note, most big rig trucks have high pressure pneumatic starters.

Hit Man X · #5 03-21-2005, 12:42 AM

My question is... where would you put the second battery?

I really don't see the need for dual batts, just get a strong single and a good alt. I found a place that'll build a 90A in the stock case... not great but better than 65A. Vehicle was engineered for a single battery

Brian Carlton · #6 03-21-2005, 01:13 AM

Quote:

Originally Posted by turbodiesel

Wouldn't give any advantage.. if you have problems starting your car, you need to find the source of those problems (glow plugs, starter, compression, etc). Mercedes designed the electrical system to work perfectly starting the car.

Sorry John, got to strongly disagree with you on this one. If this fellow is going to routinely be starting in below 0°F. ambients, a single battery is definitely marginal unless the engine compression is absolutely at the top of its range.

For an older vehicle with some hours on the engine, it may need 15 seconds of crank time at these (or lower) temperatures. A single battery is very much up against the wall under these conditions. The battery output is severely reduced due to the cold and the requirement from the engine for the maximum possible crank speed is increased due to the heavy suction of heat by the cold block.

Two batteries can maintain a higher voltage for a longer period of time. This benefit cannot be easily dismissed when starting these engines at 0°F. without the benefit of a block heater.

turbodiesel · #7 03-21-2005, 01:19 AM

Alot of people have these cars in VERY cold climates.. you don't see them installing an additional battery. Even parts of Europe get extremely cold, where many more diesels lived than over here. I've never had a problem starting any of my diesels in 0F temperatures.. The car is designed to start with one battery if all systems are operational. Sure, a 2nd battery couldn't hurt, but it isn't needed if all systems are in working order, in my opinion.

pawoSD · #8 03-21-2005, 01:30 AM

If the temps were -5 or higher I wouldn't be worried so much, but I'm talking about being parked 2 miles from lake superior, I may have days where its -15 out and I need to use the car. Mine is able to get going fairly quickly when its -5 or higher, but below that seems to be the threshold where the battery gives out before I can get it firing good enough to start.

Brian Carlton · #9 03-21-2005, 01:30 AM

Quote:

Originally Posted by turbodiesel

Alot of people have these cars in VERY cold climates.. you don't see them installing an additional battery.

They generally use a block heater, and/or don't shut the engine off for more than four hours so there is residual heat in the block.

I can't imagine attempting a cold start every morning at -10°F. without the benefit of a block heater. It would have to be touch and go with 15-30 seconds of crank time.

I still recall starting the SD around 8°F. Slow crank speed and at least six seconds before it would fire. Every degree below this makes a significant difference.

Brian Carlton · #10 03-21-2005, 01:33 AM

Quote:

Originally Posted by pawoSD

If the temps were -5 or higher I wouldn't be worried so much, but I'm talking about being parked 2 miles from lake superior, I may have days where its -15 out and I need to use the car. Mine is able to get going fairly quickly when its -5 or higher, but below that seems to be the threshold where the battery gives out before I can get it firing good enough to start.

To attempt to start a diesel under these conditions is absolutely brutal for a battery. Using two batteries would provide a higher initial voltage to the starter, thereby increasing crank speed, and would additionally provide double the crank time before the juice runs out.

pawoSD · #11 03-21-2005, 01:37 AM

I've been reading the weather almanac for Sault Ste Marie MI to see what the temp extremes usually are, and some of the records for the winter have been as low as -40!!!!!!!!!!!!!!!!!

I wonder if a gasser would even work at those temps, probably not. Most of the "averages" however seem to be between 2 degrees and 10 degrees between november and february....thats still pretty low though. I bet I could start on one battery in those temps with a fresh valve adjustment, but I am also paranoid, and having a second one in there with extra available crank time would give a piece of mind too, since I will be in college parking lot, and not at my house where it not starting wouldn't be as big of a deal. I don't want to be sitting out in that parking lot with a dead battery.

#12 03-21-2005, 07:54 AM

but the second battery was there to power a 12 volt block heater which was controlled by an automatic timer clock on the dash, to the left of the steering, and the electical system had one of those camper type isolating systems so that the block heater couldn't draw down the main battery. I've been told that these kits are fairly common in the northeastern states and provinces and Scandinavia, especially for people who have to park all day in an open company parking lot. The extra battery was positioned symmetrically with the regular battery on the driver's side under the cowl, so I suppose that the regular fuse box had to be moved a bit, etc.

Pete Burton · #13 03-21-2005, 08:11 AM

My guess is that the space at the extreme forward part of the trunk would be a good place for a second battery. You'd want huge cable, bigger than stock to reduce resistance. That being said, you really owe it to yourself to cover the other bases too, such as glow plugs, valve and IP timing, compression check, a proper oil, etc. The compression check is, IMHO, the thing you really have to do. If it's not strong, you might want to rethink the whole thing.

80benz · #14 03-21-2005, 08:14 AM

The second battery I carry in my trunk has helped me through a cold winter here in Peterborough, northeast of Toronto. On really cold mornings (below -15c), even with the block heater running for 2+ hours, my battery just doesn't have the juice to turn the engine fast enough to get going. I keep a battery in the trunk and "jump" it to my car battery on these occasions. It gives me enough cranking power to start on these cold days.

For next winter, I'm making it official and running a wire back to the trunk where I'll mount this battery in a marine-type battery box and ground it locally in the trunk.

In other words, I say DO IT!

boneheaddoctor · #15 03-21-2005, 08:17 AM

And keep in mind....if you run parrallel batteries remember when replacement time comes you have to replace them in pairs...even if one dies becasue the weak battery will drain the strong battery.

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