I recently received a message from a member asking me some questions on the batteries in our trucks. He pm'd me because he felt that it was a foolish question to post a thread about. I told him that to me there are no "foolish" questions.

I decided to answer here for all of you. I hope that is of help.

Diesels are high compression engines and take alot of amperage to start.Just look at the size of your starter. Add to that you have 8 glow plugs. They are nothing more than electric heaters.
When it gets really cold or even chilly batteries actual start to lose some of their (CCP) cold cranking power It comes back when they warm up. (charging). .The colder it is the less efficiant the battery is.This is why batteries are rated in CCA {cold cranking amps) Remember the most difficult part of a battery's life is when you are cranking over the engine, where it receives no help from the alternator. That much amperage being sucked from the battery is incredibly hard on it, which is why there are two batteries to begin with.
The batteries are wired in parallel, not series, if wired in series you gain nothing in power just the voltage doubles.This is done so the load is distributed equally to both batteries. An old battery will always be weaker than a new battery. This causes strain on the new battery This is caused by it needing to compensate for the weaker old batter.The old battery will eventually draw the new battery to the same level, or possibly weaker than the used battery. The used battery will then have to compensate for the new battery until it becomes the weaker one again., This cycle will continually repeat itself until both batteries have no "life" left in them.

Another point to ponder is the connections. They must be good and clean. You can have the biggest batteries in the world but without the proper connections they aren't going to do you any good. Make sure there is no corrosion on the terminals or cables.If you replace a clamp and you strip back the cable and notice it "green" or "powdery" consider replacing the cable itself. This is a sign of corrosion, which equals resistance.When replacing a cable it is ok to go to the next larger size cable, (less resistance), but never drop down in size.(Resistance and amperage become an issue here) Corrosion or reaistance is not good, especially when you need maximum power from your batteries to your starter. This includes the grounds. Most people just look at it as 'it's only the ground" On a DC system the ground is just as important as the positive, The ground is the return path for the electricity. Electricity needs a complete path or circuit in order to work. So the ground is essential to the system as well.

 

Nice writeup Jim! I guess I'll go out and service my.......oh wait, I have OPTIMAS

 

Great post Jim. And I could rep you too...!!!

 

Jim, this will help lots of people on here. You are the ELECTRIC MAN, for sure.

 

Thanks Rick. It took me a long time to word it the way that I wanted. I'm better at doing than explaining.

 

Great post Jim. You're the MAN!

 

Great post Jim, great explaination.

 

Good detailed explanation, thanks!

 

Excellent post, Jim. I can't rep you either, so I'm off to spread some around......

 

Jim,

That sez it all. Good job. I know first hand what weak batteries can do (and not do) after fighting my battery drain problem a while back. While I was chasing it, I cleaned ALL of the ground connections. There are more than you think ! Anyway, thnks for taking the time to help others. You are right, there are no dumb questions.
Bob

 

Thanks Everyone. I'm glad that all of you found it helpful and informative!

 

Thanks for that megawatt00, I was just going to post a battery question, you answered it very well.

 

Jim, this is the time of the year that the winter questions come up. Can't start, slow start, smoking after start. You need to start a thread on WINTER PROBLEMS. I wish I knew how to merge your post into a new thread for the Winter Thread. Good job.

 

Jim,
Speaking of batteries - what do you think of this.
I thought I had an alternator problem and it turned out to be a battery issue.
Well, I had the batteries load tested and it turned out that the "primary" battery had become very weak, but the "secondary" battery was fine. I however, replaced both batteries.
Now, I periodically switch the two batteries - reasoning is that I think even though they are in parallel, the primary one tends to see more drain, use or whatever you might call it. Maybe that's why they call them "primary" and "secondary" batteries.

Just some observations,

 

Very good observation. The distance between the batteries isn't so great that there will be a huge difference in the drain between the two. There is nothing wrong with switching the two of them around though. Therotically the battery that the starter is teid into will "get" more drain. You can also increase the wire size on the wire going between the two batteries, or parallell the existing wire. The ideal set up would be to center tap all of the feeds from inbetween both batteries.