Can an optima red top battery be combined (in parallel) with a standard sears diehard without one attempting to drag down the other?

Love the on board air. What are you using it for? does your small compressor and tank provide enough for short bursts with air tools? Are you just inflating things? I've been thinking about a compressor & tank set up for my truck for inflation of float bags (canoe) tires...What sort of compressor do you have there?

AS for dual batteries? I like the idea but need to get my car running properly with 1 first:rolleyes:

Not unless they are electricly isolated from each other...

The optima charges to a slightly higher voltage than your average lead-acid battery...

Pairs of batteries hardwired together need to be same age and same type....

How do I know...read my sig....I have a Truck with dual batteries..(and an electronics degree)

better watch your daughters.


:D :D

I bought a 12 volt Thomas compressor on eBay that will push up to 120 psi. The tank was a small one that I bought locally and its great for an air horn. You can also fill tires with it and I use it for blowing leaves out of the places where they love to fall and get trapped (every Mercedes I've ever owned has several places for leaves :( )
I have no plans to even try using an air tool on it, unless it was a nailer maybe, because anything that uses lots of air will cause the compressor to run all the time, and these are intermittent use compressors. Besides they draw about 15 Amps, they run hot and the motor will die if it runs continuously.
There are two ways to plumb air up to the front (unless you wanted rear facing horns?) One is to send pressure up front and put the solenoid valve on the horns, its short wiring hop. The other way (which I am using) is to place the valve at the compressor and run wires back to it from the existing electrical horns, this way the pressure is not on that line all the time and I think it will be happier and last longer in the long run. Either way you have a small hose to run. I used 1/4 in black cpvc because the white semi translucent pvc hose isn't any good because it will crack from exposure to UV

The use of a second battery is no problem as long as you use a battery isolator. The two batteries can be different as long as they are charged through the isolator and they require the same or very close to the same charging voltage. Sure Power makes a good isolator.
One important note: DO NOT hard wire batteries in parallel, that's askling for a disaster when/if one shorts it will pull the other down and one of them usually explodes and spurts acid all over everything. This was a big mistake that Cadillac made in the '83 Diesel Brougham (besides trying to make a diesel engine!). I knew someone who had that happen in one and it wasn't pretty!

Cadilac never made a diesel engine.....Detroit diesel did.........

Well, you know what I meant!:rolleyes:

Be weary of eletronic (solid state) battery isolators. When I worked at the auto electric shop we had a lot of them come in bad.

The best way to do it is just put a large solenoid that connects the two batterie s when the car is running (or the key is on/start mode) and disconnects them when sitting.

You generally don't want two batteries in parallel sitting without any imput amperage to both of them. They will feed off one another (so to speak).

On our camper/truck, when you flip on the key it connects the two batteries in the engine compartment together (and one of those is connected to ANOTHER battery in the camper).

So you have 3 batteries all hooking up in parallel to fire the engine.

Now keep in mind...if you run one of your batteries down with a block heater or whatever you might be running off of it, you probably want the ability to get your car started WITHOUT connecting to two together becuase the 1st batt (charged) will feed the 2nd discharged one and all your power is going where you don't want it (when trying to start).

Sorry if that is confusing...I think two batts is a good idea but for where I live and whatnot, it rarely drops below the teens.

An intake heater might help your rig start (in addition to the glow plugs). I would look into that before putting 00 gauge wire from trunk to front...that stuff isn't cheap ;)

Yes, it does get cold up there!
 

But there are a lot of colder spots in North America then the UP of Michigan. I lived (as a child) just outside of the Soo as it is known, in the little town of Rudyard. Lots of snow and some dandy wind chills, and a couple of days a year ambient temperatures that will really try the soul of any diesel or diesel owner.
So how about this as a low cost easy solution. A quality battery in a case that has a handle, a pair of quality and short jumper cables and a small trickle charger. Keep the battery charged up and warm and when ready to fire up the SD, quickly hook on that warmed up battery with 650 CCA. When it has started and is running well, tuck the assistant battery in the trunk along with your jumper cables and later or the next day, while you do your studies, bring that battery back into the apartment and give it a charge. Batteries do vent a little acid vapor, but I don't think enough to be hazzardous if the charging is done while you are awake. I really think a small but warm "quality" battery could really make a difference.

A warm battery is much stronger than a cold battery that is a law of physics.
A person who carries batteries around frequently has bigger arm muscles than one who doesn't esp when a group 49 battery is involved. This law of nature.
If you decide to carry a battery in a battery box out to your car frequently, please be sure you install the battery in a battery box and lash it down using wide nylon straps over the top of the cover for it.
Otherwise, one quick swerve to avoid a pot hole or a car that tries to pull in front of you or something and you're likely to have a battery fly across the trunk and punch a dent in the trunk from the inside (I've see that before its not a pretty thing!)
Sorry but I have to vote against this solution.

Or chemisty :)

Would a basic Ford starter relay (or glowplug relay) that switches on with the key, work for starting and charging? Could I run the stock MB battery with a different model battery in the trunk (Think standard 700-800cca auto battery)?

But.......
 

I have to disagree, go and put a voltmeter on any hot wire in the car. When the gp's are engaged, voltage drops to any where between 10.5 to 8.5 volts. Having two batteries would mean twice the amperage supply, and half the load on each battery, which will reduce voltage sag, and increase voltage to plugs. Viola! more heat!

Simple logic....

It doesn't have to be a grp 49 battery
 

There are plenty of smaller batteries around that could give an large boost to any "nearly frozen" battery. And I think in the neighborhood of 20 to 25 pounds. But of course there are people who can hardly carry their own weight. I know that. But PawoSD seems to me to be a very active young man. And I would be surprised if he found carrying a small battery in a plastic case, say up to 1200 ft or two city blocks that difficult. But again maybe he would. That is his choice. But it is easily workable and not really expensive.
Regarding putting the battery in the trunk for a couple of hours, that too is a lot of hogwash. Batteries are tough and you can easily use the jel filled so there is no need to have battery acid running over the trunk. On his return trip he might be able to park very close to unload the battery back in Apartment or dorm. The cables will stay in the car. Now on my W123, there is a nice lower trunk floor on each side and that would nicely hold a battery from sliding around. I think PawoSD has a W124 and I don't know if that trunk floor has that arrangement. Also, I am old enough to know that these low tech "armstrong" solutions usually don't fly well. They work, but it's too simple.

I measured 11V at the GPs on my 300D while they were glowing, which is what they are rated for (with a single Interstate battery, about 1 year old). I suspect any modification that increased the GP voltage above 11V would also shorten their life. BTW, I have a small trickle charger installed next to my battery. Whenever it's cold enough to use the block heater, I also plug in the charge. It makes sure the battery is fully charged and keeps it warm.