mstep3

This may be a dumb question, but what's the purpose of having 2 batteries installed in the 2500. Did most of the 2500's come from factory with 2 batteries?

I got an 02' & have never replaced the batteries on it. Getting close to having to replace them.....

catnfool

well, since the older cummins only had one, I put 1 high dollar Oddesy battery in my 98 12v. It does not turn her over with authority when it gets cold out, and I am going to have to go back to 2 this winter. WHICH is a shame, because it is SO much easier changing my oil filter with that batt gone

XLR8R

The "extra" battery on the CTD Rams powers the grid heaters.

jrs_dodge_diesel

The second battery doesn't just power the grid heaters alone. Both batteries power the entire truck.

Technically speaking, the batteries are wired in parallel, which keeps the voltage at 12V, but doubles the amount of available current (amps).

As noted above, you can run one battery, but come winter time, the battery will not have an easy time providing enough power for the grid heaters and starting.

The 1st gen Rams with a Cummins only had one battery to my knowledge. Starting in 94 (the first year of the 2nd gen), 2500 and 3500 trucks with the Cummins have 2 batteries.

XLR8R

Driver's battery starts & runs the truck fine, but you need the 2nd battery's ampacity for the grid heaters.

jrs_dodge_diesel

Ampacity ??? Ampacity is the current(amps) carrying capacity of a given cable. That has nothing to do with batteries.

The grids draw between 150-200 amps (quite a load), but nowhere near the full output from a single battery. Let's take the red tops in my truck for example. Just one is rated for 800 CCA (cold cranking amps) and 1,000 CA (cranking amps). That is the rated current a battery can provide for 30 seconds continuously while maintaining 1.2 Volts per cell (for 12 Volts total) at 0°F and 32°F.

What I am getting at is that a single battery can handle the load (as they do in 1st gen Rams which also have grid heaters). Having two just doubles the amount of available current. Again, using my red tops for example, my CCA is 1,600 amp and my CA is 2,000 amps. All that happens here is now the load (grid heaters, starter, truck) is shared between the two batteries and puts less demand on each battery individually.

Tate

I have on battery in my dually. It will fire up when its cold, but it doesn't like it. If you are running 15w40 oil when it gets cold, good luck getting it started with a single battery unless its is a big one.

Astro

I run two batteries in all the diesels I've had. My 1st gen had a single, I converted to dual Optimas. My OBS P-Stroke had duals, I replaced with dual Motorcrafts, and my '97 Dodge Dually has dual batteries stock. It barely cranked when the pass side battery took a dirt nap, but it would hold a charge once running. I replaced it with a $100 parts store battery and it cranks up like it should.

patdaly

Why?

Because 30 below is no time to have to worry about "Will she start?"

XLR8R

I agree JRS - just trying to keep it simple for the OP... simple answer is "grid heaters".

I view ampacity as the current-carrying ability of a circuit, and include the battery as part of it.

jrs_dodge_diesel

Ahh, I see.

That's does simplify things. I think I was looking at it from a technical perspective.

Dave2001

"jrs dodge diesel" hit the nail on the head.
Paralleling gives a larger reserve capacity if you need it.
When would you need this extra capacity? In the winter time when the grid heaters are on and cycling, the starter uses more current to start the engine, the headlights are probably on, and the blower motor is probably running, etc.
By paralleling the batteries you help limit the current drain in each individual battery. This means each battery does not require as much charge to be back at 100%. A small short charge on the battery is less likely to boil off the liquid in each cell.
Sure you might get by on one battery, but you are much better of with the second one.

Lil Dog

Having one battery being able to handle the hard initial draw of the grid heaters of 100 amps for 30 seconds and then provide the starter with enough juice to turn the engine over with ample speed is great if the Optimas can do it.

As Dave2001 illuded to, the problem is doing it every day, sometimes 2 or 3 times a day will kill the battery. Full draws and charges repeatedly at over 50% capacity of the battery will shorten its life significantly. Having 2 batteries with the capacity not only allows for less drain on one, but not stressing the batteries every start.

I had 2 first gens, an 89 and a 93. The 89 had a huge battery, but they didn't last very long. I had paralleled two 1200 cca batteries in my 93 and never had a problem for 4+ years.

I made a mistake and bought lower level batteries for my 97 and will probably be replacing them shortly as I also run an Espar heater in the winter. That will put a drain on the batteries pretty quickly as well.

Dave2001

Speaking of longevity of batteries. My truck still has the original batteries. I expect that they will die in the near future.
Automotive batteries, the lead-acid type, provide a nominal 12-volts by connecting six cells in series. Each cell provides 2.1 volts for a total of 12.6 volt at full charge. Automotive batteries usually have a greater plate count in order to have a larger surface area that provides high electric current for a short period of time. Hence the cold cranking amp rating.

mstep3

Thanks for the information on this.....I guess the only reason that I was wondering is because I live in the south. It usually does not get below 25 - 30 degrees F where I'm at. I was just wondering how a truck would fare in that kind of weather with one battery in the winter.....