# TLS's GM Dual Battery How-To....



## TLS (Jan 31, 2000)

The following will be a pictorial showing how I installed dual batteries in my Gas Engined '04 GMC 2500HD.

First of all, you'll need the following tools:

3/8" ratchet
3/8" extension
10mm Deepwell socket
13mm Deepwell socket
10mm combination wrench
13mm combination wrench
5/16" battery wrench
9/16" combination wrench

You will also need the following from your GM dealers parts counter:

15705102 Battery tray ($20.31)
356668 Battery hold down V-Clamp ($5.61)
11509853 Battery hold down bolt ($0.65)

You will need a Group 34/78 Side/Top post battery. In my case I used matching Optima Red Top batteries from Battery Mart.com










I searched locally at several different locations. NONE had 2 that had matching build dates. Most locations only had ONE. NONE seemed concerned when I asked if they had others in the "backroom", or offered to order some in. I paid $250.57 for two matching Optimas shipped to my door.

You will also need some various lengths of battery cable. I used some leftover from my BOSS Snowplow install, and also have access to other. I used a store bought preformed 24" side post ground cable.

Here is where the new tray will go.


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## TLS (Jan 31, 2000)

This black firewall to fender support will be removed and discarded.

Use your 13mm socket/ratchet to remove bolts. There are no nuts, they're built into the support.


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## TLS (Jan 31, 2000)

Personally, I removed this mounting tab. It makes dropping in the battery a little easier, and if your not using an Optima battery (which has inboard mounted top posts) it will give you more clearance to mount a top mount battery post clamp on the negative post.

Now also remove the 4 mounting nuts attaching the fender bracket to the firewall which are shown in this picture as well.

You also have to remove the radiator overflow tank and its hold down nut (10mm)


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## TLS (Jan 31, 2000)

This is your battery tray, hold down clamp, and fastner. Total cost = $26.57


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## TLS (Jan 31, 2000)

Then, simply install new tray using the existing firewall studs and nuts.

All thats left is to install the new battery.

I used a quality pre-formed 24" negative cable found in auto parts stores. I went from the aux. battery to the passenger side engine head accessory hole. You can see it go between the dipstick and the oil-fill cap. It is the black wire with the heat tape around it.


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## TLS (Jan 31, 2000)

I ran the wires across the cowl using insulated metal cable fasteners.

You could also run across the radiator support. It really doesn't make much of a difference.

I mounted my plow solenoid under the drivers side fender support, and found it easier to run everything across the cowl/firewall.

Be cautious running wires in these area's, as the hood hinge spring suprisingly takes a large swing.


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## TLS (Jan 31, 2000)

Then I removed the wimpy 









600 cca AC Delco factory battery and replaced it with the other matching Optima Red Top.


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## TLS (Jan 31, 2000)

For attaching cables to the side posts, I prefer to use 3/8" stainless steel bolts and nut.

Screw a nut on the bolt all the way to the head. Then insert that bolt/nut combo into your cable eyelet, then thread it into the batteries side terminal. Snug it, but don't get too crazy, as your going into a soft lead. Then tighten the nut towards the battery snugging the eyelet to the battery.


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## TLS (Jan 31, 2000)

The above shown method of installing dual batteries is know as the parallel method. They are NOT isolated, but instead are hooked up positive to positive negative to negative. This gives me 1600 Cold Cranking Amps (cca's) versus the original factory battery supplying only 600 cca's.

Startups are snappier, plow raises quicker, lights dim considerably less, and voltmeter doesn't drop like it did with just the single battery.

This setup, combined with my 145A alternator should provide pleanty of power for plow, spreader, lights, and accessories.

I hope this helps those of you with '01 through '05 GM trucks that weren't equipped with factory dual batteries.

Total cost for me was less than $280.

You could do this for under $175 if you choose to use standard lead acid batteries insead of the Optima's.

If you have a brand NEW truck, you could feasibly do this by simply buying another AC Delco battery and using it for your aux. battery, and saving even more money.

Best bet is to order the dual battery option from the factory and modifying it to a true parallel setup.


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## TLS (Jan 31, 2000)

Thats about all for now.

Not totally step-by-step, but the info is there for your use.


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## OneBadDodge06 (Sep 22, 2004)

do you really notice a big difference using an optima instead of the stock battery?


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## TLS (Jan 31, 2000)

blade_masters said:


> do you really notice a big difference using an optima instead of the stock battery?


Absolutely!

600cca VS 1600cca

Plus I've found that dual batteries tend to last longer than single.

And from what I've heard, Optima's tend to last longer than your typical lead acid battery. Shock and vibration is what will kill a battery. You cant get much more shock and vibration than a plow truck.


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## REAPER (Nov 23, 2004)

_"Plus I've found that dual batteries tend to last longer than single."_

That is a very true statement. I have dual's in my 88 GMC. One battery was new in 96 the other 97. Both have plowed every season since. They both still test at 90% power of new. Both are Interstate 1000CCA..


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## OneBadDodge06 (Sep 22, 2004)

TLS said:


> Absolutely!
> 
> 600cca VS 1600cca
> 
> ...


Yeah I can see your point. I got a die hard heavy duty b/c of the rockin and rollin. Has a heavy duty case and cells. I just thought that an alternator can only crank out so many amps so it's like trying to fill a water tower by pee'n in it


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## TLS (Jan 31, 2000)

blade_masters said:


> I just thought that an alternator can only crank out so many amps so it's like trying to fill a water tower by pee'n in it


That's not a good analogy really.

A dual setup will take repeated hits of lifting and angling without draining as far as a single battery, thus acutally extending the life and load on the alternator. In essence, it won't be working as hard because the nominal voltage didn't drop as far down.


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## Bad Luck (Sep 30, 2004)

Nice set up and tutorial TLS..  

Since doing mine, I re-ran my cables under the radiator cover, and moved my ground to the block. Much more clean looking. Question: What did you do about the factory battey cables on the driver side battery? Did you cut off the factory end and add your own eyelet? I wanted to use a bolt to attach the cables to this battery but was leary of doing so.


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## TLS (Jan 31, 2000)

For now, this is what I did....


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## TLS (Jan 31, 2000)

Sorry, I just realized I posted the picture and didn't type in my explanation.

It was getting a bit late last night on that last post.

I used the lead collar spacers supplied by BOSS to extend the side terminal's enough to accept an additional terminal. They give you a couple of these collars, and a couple of side terminal extention bolts.

I still may end up using the top terminals eventually. However, finding good quality top terminal battery connectors isn't easy. Most are crap "Made in China" stuff.


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## Frozen001 (Oct 20, 2004)

TLS said:


> I still may end up using the top terminals eventually. However, finding good quality top terminal battery connectors isn't easy. Most are crap "Made in China" stuff.


Have you tried looking at a high end car stereo shop or supplier?? they usually have some quality products.... just a thought...

Lou


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## TLS (Jan 31, 2000)

Thats a good idea. Sadly though most stuff such as this is overly ricey. GOLD plated  .

I just want a nice HD top mount battery connector.....preferably with a matching positive protective plastic cover.

Right now, everything works well. Just want to put some finishing touches on it.


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## CyberJay (Jan 16, 2005)

wrangler nw has some "military" top mount connectors that seem real nice. I haven't installed mine yet. Cheap, not gold, should work real good.

www.wranglernw.com

-Jay


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## TLS (Jan 31, 2000)

I really like this one.










Looks like you strip your battery cable, insert it in the collet and tighten it down and it crimps and holds in one step.

Problem is, it's only for Negative posts. 

Maybe I'll give them a call after I take my nap!


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## The Boss (Oct 22, 2003)

Tommy, try the audio dept. at a local Best Buy if you have one near you. They have all kinds of that stuff. By the way, very nice information you put on here. I must say it was excellent that you put all the needed tools in it as well. Great job!! :waving:


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## TLS (Jan 31, 2000)

Thanks for the props Boss!  

I'll take any excuse I can think of for a trip to Best Buy. Thanks for the tip. These ricers gotta be good for something, right?


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## djd427 (Dec 19, 2004)

TLS,
Thanks for posting the pics!!!! You made it easy. I just bought a 05 2500HD a few weeks ago. The dealer(owner) pulled the battery and gave me 2 (same date) As soon as I got home from the dealership I swapped the one in the 04 3500 and put that one in the 2500. I am just about done installing the second one in the 3500. (just have to make connections) He also gave me another tray for the 2500. He told me when I am ready, "stop by and he'll give me 2 more for the cost of one. (taking the one from the 2500). 

Thanks again!! You couldn't have explained it better. I owe you one


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## The Boss (Oct 22, 2003)

TLS said:


> These ricers gotta be good for something, right?


LMAO, I'd say that's the ONLY good thing.


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## topdj (Oct 6, 2007)

my 07 has a extra tray, I added a marine switch and diode to keep the 2nd battery charged


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## cjasonbr (Nov 18, 2005)

It would have been interesting to see what the difference between just replacing the factory battery with an optima vs adding the 2nd optima would be.


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## ford6.9 (Aug 17, 2006)

I just want to thank you, people like you sharing information as little as it may be helps us all grow. Funny as it may be i never grew up with someone to show me how to do all this little stuff, and have learned most i know off this website along with a few others and lots of hours working on stuff and just wanna thank you and everyone else who has shared information and spent the time to share, pictures and all.


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## mike1316 (Sep 16, 2007)

yea thanks guys


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## RichG53 (Sep 16, 2008)

One other thing you should do according to B Bis run an additional 4 gauge wire from your alter to the battery...I'm doing mine soon nice job ( I don't liker red trks HA HA)


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## Saltydawg (May 12, 2008)

Don't forget a big old tube of dielectric grease. This stuff is pure gold for protecting electrical connections.

I squirt some in every electrical connector I can reach. Any exposed connections such as battery terminals and large relay connections get a liberal coating of it. This will pretty much prevent 90% of electrical problems.


edit: On my hydraulic pump that sits out front on the frame I don't use the grease cause it just gets washed and worn off too easily. Up here I wire brush and clean the connections really well with a good electrical cleaner then I use liquid electrical tape like is used in marine applications. Works good.


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## sanbar406 (Nov 4, 2015)

*2004 GM Truck Dual Battery*



TLS;205882 said:


> This black firewall to fender support will be removed and discarded.
> 
> Use your 13mm socket/ratchet to remove bolts. There are no nuts, they're built into the support.


Question: How can you have discarded the curved support bracket? It's structural to the vehicle.


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