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Old 01-04-2014, 10:52 AM
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Charging System- "Outside The Box" Question

I'll preface this conversation with the understanding that I know nothing about electrical systems. I can troubleshoot and solder, etc, but that's about it.

A co-worker has a '97-ish GM Tahoe with dual batteries. He got surfing the web and discovered a "GM Engineer" created a mod for better charging in dual battery vehicles.

From his alternator, there are two red (POSITIVE) cables. One goes direct to each battery. Apparently this enables the alternator to charge each battery equally.

So, since my truck ('95 F250, 7.3) either has battery or alternator issues now, it's time to crack this nut before I go shopping. I will functional check my batteries and alternator separately. Just want to know your thoughts on the topic.

Any suggestions? Which would work best: stock charging system, or the "GM Mod"? Pros/Cons?

Oh dumb question alert: I've never had to jump-start a dual-battery truck before. Which battery to I hook the jumpers up to???

Thanks in advance!
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Old 01-04-2014, 11:01 AM
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I've used either battery to jump a truck, but when it's real dead I've used 2 cars hooked to both batteries, the idea is sound tho on the "GM" mod, but my brother does stereo and recommends increasing the wire gauge size for ground, positive, and alt to battery(ies)
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Old 01-04-2014, 11:46 AM
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I dont think it really makes a difference until you start talking about isolators or moving batteries out of the engine compartment.

The amount of wire to run them directly from the alternator or in series wont gain you much IMO.

Your money is best spent in a high output alternator and large gauge wire with good connectors.
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Old 01-04-2014, 12:07 PM
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common on Ford to upgrade the wiring also but in an OEM application without extra loads
you won't see a benefit unless your OEM cables/connections are compromised

like mentioned
the batteries also don't know the difference if the lead goes from the ALT to one positive terminal and then from terminal to terminal on the batteries
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Old 01-04-2014, 12:51 PM
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Quote:
Originally Posted by 351fifty View Post
I've used either battery to jump a truck, but when it's real dead I've used 2 cars hooked to both batteries, the idea is sound tho on the "GM" mod, but my brother does stereo and recommends increasing the wire gauge size for ground, positive, and alt to battery(ies)
I had to ask, thanks for the reply!

Quote:
Originally Posted by Heavy_GD View Post
I dont think it really makes a difference until you start talking about isolators or moving batteries out of the engine compartment.

The amount of wire to run them directly from the alternator or in series wont gain you much IMO.

Your money is best spent in a high output alternator and large gauge wire with good connectors.
Quote:
Originally Posted by ZMANN View Post
common on Ford to upgrade the wiring also but in an OEM application without extra loads
you won't see a benefit unless your OEM cables/connections are compromised

like mentioned
the batteries also don't know the difference if the lead goes from the ALT to one positive terminal and then from terminal to terminal on the batteries
Thanks for the quick feedback!
So, the GM mod is basically a "preference" scenario? meaning: it doesn't really MATTER, just as long as the cable connecting the batteries is working properly & is of the correct size?

My cables looked surprisingly well, the connectors...well, they're debatable.

I couldn't find my Fluke-meter to check the batteries.

So, I hooked up the battery charger. Passenger Side Battery (assume this is Primary) was around 75%. When it charged, I hooked the charger up to the Drivers Side Battery (assume this is Secondary?). It was at about 25% charge. What the???

Batteries are dated 11/11, but they are cheapo WalMart 750CCAs. I've got to check the warranty on them. .

I'm still going to clean things up and get everything tested out. That was a significant shift in charge capacity between the two batteries.

After I know my alternator and batteries are good ($$$), I'll go to Rock Auto & buy all new OEM-type cables. Don't have time to build my own...

I'll let you know what I came up with. Thanks again!
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Old 01-04-2014, 05:22 PM
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I can't speak to the "preference" part because they may be eliminating a weak link on the Chevy.
For our trucks its fine.

Be careful with those batteries they can start fine but over work the alt
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Old 01-04-2014, 05:45 PM
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750 CCA is insufficient for our trucks. 850 CCA minimum.
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Old 01-05-2014, 10:36 AM
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Quote:
Originally Posted by Heavy_GD View Post
I can't speak to the "preference" part because they may be eliminating a weak link on the Chevy.
For our trucks its fine.

Be careful with those batteries they can start fine but over work the alt
Copy: Chevy= weak link

Quote:
Originally Posted by madpogue View Post
750 CCA is insufficient for our trucks. 850 CCA minimum.
Well, that would explain a LOT! Guess I need to read more! Thanks for the save on that one!

All my connectors were in good shape. Minor corrosion. Cleaned up the connectors, battery posts, and as many grounding points that I could access real good, new bolts on the connectors. Cranked right up. I'll get it load tested this week.

And will have to see what I'm going to do about 750 vs 850 CCA situation.

Thanks again for the solid advice!
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