# Dual battery "How To"



## gcsupraman (Apr 28, 2004)

I just did the stock dual battery conversion and I found this modification so "worth it", I wanted to share with you guys a very simple "how to"

This is for a 2002 (or similiar) 2500HD:

I have a fisher X-Blade which easily overwhelms the stock 600CCA battery (when I would use the plow, the lights would severly dim). With the 8.1 liter motor, I thought the battery was to small anyway as it strugled in the very cold weather to start the truck. Well this morning, after installing the dual battery setup, I started the truck and it's a whole new truck! It starts much better than before. I would highly recommend this mod to anybody with a 2002 or similar truck. For less than $150.00 it was well worth it.

Let me explain how I wired the battery. I left all of the original battery connections in tact - I didn't touch them at all. I installed the stock aux. battery tray I bought from GM (about $25.00) and mounted a OEM Delco battery on it. You will also need the clamp that holds the battery down and the bolt that holds the clamp to the tray. Installation was very easy and straight forward. Using bulk "Monster Cable" brand 4 gauge wire that I purchased from a car stereo shop, I wired the positive side of the aux. battery directly to the starter. The stock battery is directly conntected to the starter as well. There is a 13mm nut holding on the stock battery positive cable to the starter. I removed the nut, slipped on the 4 guage wire going to the aux battery (which I put a "Monster cable" brand 4 guage ring terminal on the end) and put the stock nut back on. I then wired the negative side of the auxillary battery to a bolt located in the front passenger side of the engine block.

Using this setup the batteries are directly connected (in parallel) to each other at all times. This setup was extremely easy and required minimal technical ability. I use the truck for plowing and do not need the isolation setup for accessories. I need both batteries on at all times.

It's a great mod - especially since it's only $150 (less if you don't buy a Delco battery) I would highly recommend this anybody with a plow.

Hope this helps.

-Greg


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## streetsurfin' (Jan 22, 2004)

It sounds like you have the wrong idea of what an isolater does. That's fine that you chose not to use one, though. Isolating them will let them drain seperately. It would allow you to use one battery for plowing while using the other for the truck. Each will charge at independant rates as needed. Should you develop a problem with the plow, that used more juice than you could replace, you'd still have some life left in the truck battery to keep you going. In the same case without an isolator, both batteries would be drained.


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## Turfmower (Dec 20, 2003)

You don't need an isolator, its for running lights and such on campers so you don't kill you starting battery. 
For plowing hook both battery positive to positive and hook the ground of the new 2nd battery to the frame. You will get the power from both batteries to run your plow/salter.


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## BigRedBarn (Jan 4, 2003)

I have the dual battery set up from the factory and find it works fine. I went with 2 batteries as my old truck had trouble powering the plow and the lights and and and. 

I guess I'd use the isolator if I did the installation myself, too. If the main battery goes dead you can always do a jump start off of your second battery, right?

I do find that the 2-battery truck seems to do a lot more battery charging (per the voltage gauge) after start up, especially if the truck's been sitting for a few days. If I turn on the lights, and have the heater switch set to a defrost mode (where the a/c compressor runs?), it seems like the serpetine belt squeals a bit, especially in really cold or in really damp weather. 

That's just my 2¢.


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## TLS (Jan 31, 2000)

gcsupraman,

While in essence you _did_ hook them up in parallel. However, I would suggest just running a 4 gauge (or even heavier would be better) wire from POSITIVE + of original battery to the POSITIVE + of the new battery in the $25 aux battery tray. Your method, though seldom used does the same thing.

I will be doing the same thing (have battery tray mounted, removed fender brace and sheet metal bolt lip) I even have a heavy cable made. Just need to go buy 2 new Optima red tops as they have side AND top mounted posts. I'll hook the parallel connector up to the top posts and all accessories up to the side posts.

I took pictures during the installation of the tray, including removing the sheet metal tab and fender brace. I'll post a write-up as soon as I complete the whole package.

BigRedBarn,

The factory aux battery setup from GM isn't a Parallel system. It's designed for isolation and doesn't link the batteries in parallel for the heavy surges that plowing induce. You would benefit greatly from adding a cable from positive to positive and one from the aux to the block for the negative. Your truck will start much quicker, and you won't see that voltmeter struggling anymore.

GM needs to understand this and offer two types of hookups. One for camper guys that NEED isolation, and one for snowplowers who need the capacity of two batteries acting as one.


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## djd427 (Dec 19, 2004)

TLS,
pictures please. I already bought a gm tray but didn't get started on it yet. 1 question, The truck only has 1600 miles on it, do you think I should buy a delco to match or just buy 2 news ones?
Thanks Dave


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## GPB (Dec 17, 2003)

TLS,
I have the factory aux. battery in my 02 Chevy. The only time the battery is isolated is when the key is off. Turn the key on and both batterys are hooked together and available for plowing. If I happen to forget to shut my lights off, only 1 battery will discharge as long as the key is off. 
Why is this not a good set-up for plowing?


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## TLS (Jan 31, 2000)

GPB said:


> TLS,
> I have the factory aux. battery in my 02 Chevy. The only time the battery is isolated is when the key is off. Turn the key on and both batterys are hooked together and available for plowing. If I happen to forget to shut my lights off, only 1 battery will discharge as long as the key is off.
> Why is this not a good set-up for plowing?


I was unaware that they were like that on the NBS trucks from the factory. My '90 Chevy wasn't the hottest setup and only had tiny (8g) wires running to the isolation solenoid. I guess, if they are hooked up pretty stoudt now with 4g or better, then it would be OK. Just unnecessary IMO to have them unhooked when the trucks off. I like nice heavy cable running direct between them.

djd427,
If your happy with Delco batteries, then that would be your best choice. More importantly is the actual build date of the battery/truck more than the miles. Mine had been sitting on a lot for a while and I had already accumulated 4500 miles before I decided to go dual. The stock battery is wimpy anyway.

I like the side AND top terminal batteries anyway.....Gives you 4 nice attachment points for + power, instead of octopussing everything out of one terminal.

Pics will follow, I don't want to post until I have it completed, and then I'll post a nice pictorial "how-to" on the forums. If you have any questions about the tray installation/sheet metal cutting, let me know.


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## djd427 (Dec 19, 2004)

TLS,
I am going to wait for you to post the whole project before I start, (never added another battery before) But I think I am going to get 2 new batteries with the double post also,it will seem to make add ons much easier. I think I will put the Delco in the other 3500. (They were made within weeks of each other) just incase we decide to add more to that one.
I appreciate the help, Thanks
Dave


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## gcsupraman (Apr 28, 2004)

djd427 said:


> TLS,
> I am going to wait for you to post the whole project before I start, (never added another battery before) But I think I am going to get 2 new batteries with the double post also,it will seem to make add ons much easier. I think I will put the Delco in the other 3500. (They were made within weeks of each other) just incase we decide to add more to that one.
> I appreciate the help, Thanks
> Dave


It is the easiest thing ever. I even posted a quick "how to" at the top of the page.

Unbolt the factory fender brace.
Unbolt the lower fender brace.
Bolt in the OEM battery tray. 
Put the battery on the tray and wire + to + on the OEM battery and - to a good ground.

I'll try and post some pics...but trust me it is so easy!

-Greg


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## TLS (Jan 31, 2000)

You forgot lifting up the coolant recovery tank, and trimming the fender brace sheet metal.


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## CHPL (Oct 26, 2003)

If you want to add a secound battery on right side and use factory cables without an isolation relay here are the cable part numbers
positive 15372006
Ground 15321207


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## gcsupraman (Apr 28, 2004)

TLS said:


> You forgot lifting up the coolant recovery tank, and trimming the fender brace sheet metal.


Your right - remove two small bolts from the coolant tank and move it out of the way while you install the tray.

I did not have to trim any metal - which metal are you talking about? The battery tray replaces the lower fender brace. At least thats what I read....

-Greg


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## TLS (Jan 31, 2000)

The firewall to fender curved bracket that you remove....the two bolts that attach it to the firewall, that metal bracket that those two bolts go through is NOT there on diesel trucks. I sawsalled it off, as battery installation is REAL difficult with it there.


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## BigRedBarn (Jan 4, 2003)

TLS said:


> BigRedBarn,
> 
> The factory aux battery setup from GM isn't a Parallel system. It's designed for isolation and doesn't link the batteries in parallel for the heavy surges that plowing induce. You would benefit greatly from adding a cable from positive to positive and one from the aux to the block for the negative. Your truck will start much quicker, and you won't see that voltmeter struggling anymore.
> 
> GM needs to understand this and offer two types of hookups. One for camper guys that NEED isolation, and one for snowplowers who need the capacity of two batteries acting as one.


I'm sorry, I didn't mean to imply that the factory setup was non-isolation (parellel). As far as I know, my system (factory) dedicates the 2nd battery for the plow only. It seems to work well enough.

As far as I know (and I don't know much as I barely passed all my electrical engineering courses that us mechanical engineering students had to take for some silly reason) the system type (isolation versus parellel) shouldn't make any difference as far as charging, should it? After all, you're charging two batteries regardless of how they're hook up. Or, am I missing something there? Can anyone comment on that?

I'm not sure I'd prefer a parallel system. To me, there's always a chance where if both batteries aren't in the exact same state of charge (or if they're not exactly the same battery, or if they are the same but what if one's a bit older or has seen more use) that the charge in the two batteries will equal out. That is, the battery with more charge will charge the other battery all the time. I would think that's not a good thing to have going on all the time as it would seem to use up charge as that's not a 100% efficient system. If anything, the cables would get a little warm (probably slightly, but still some). Can anyone out there verify this theory of mine?


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## TLS (Jan 31, 2000)

BigRedBarn said:


> I'm not sure I'd prefer a parallel system. To me, there's always a chance where if both batteries aren't in the exact same state of charge (or if they're not exactly the same battery, or if they are the same but what if one's a bit older or has seen more use) that the charge in the two batteries will equal out. That is, the battery with more charge will charge the other battery all the time. I would think that's not a good thing to have going on all the time as it would seem to use up charge as that's not a 100% efficient system. If anything, the cables would get a little warm (probably slightly, but still some). Can anyone out there verify this theory of mine?


This is why everyone recommends that BOTH batteries be the same type, size, brand and age when in a parallel system. All your diesel pickups, and over-the-road trucks use multiple battery systems....all run their batteries connected in parallel.

By only using one dedicated battery for the plow, your only reaping the benefits of ONE battery. When their joined in parallel, your reaping the benefits of BOTH batteries capacities combined.

Hope this helps.


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## repo_man62 (Oct 24, 2004)

TLS said:


> gcsupraman,
> 
> While in essence you _did_ hook them up in parallel. However, I would suggest just running a 4 gauge (or even heavier would be better) wire from POSITIVE + of original battery to the POSITIVE + of the new battery in the $25 aux battery tray. Your method, though seldom used does the same thing.
> 
> ...


What if you have a "storage" box like this? Can you just cut the box to fit another batt? Lower r/hand corner & upper r/hand corner respectively


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## gcsupraman (Apr 28, 2004)

repo_man62 said:


> What if you have a "storage" box like this? Can you just cut the box to fit another batt? Lower r/hand corner & upper r/hand corner respectively


I can't really tell by the pics what year your chevy is but on my 1988 (newer body style) k1500 it had dual batteries with tray's on either side of the radiator. The aux battery was right where that box is...maybe you should goto GM and see if they sell the aux battery tray for your vehicle. It would make it a much easier install

-Greg


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## repo_man62 (Oct 24, 2004)

gcsupraman said:


> I can't really tell by the pics what year your chevy is but on my 1988 (newer body style) k1500 it had dual batteries with tray's on either side of the radiator. The aux battery was right where that box is...maybe you should goto GM and see if they sell the aux battery tray for your vehicle. It would make it a much easier install
> 
> -Greg


It's a '97...would only have to cut 1 corner that's inset (for whatever reason).


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## TLS (Jan 31, 2000)

On that era truck, they used to put the AUX. battery right where your washer bottle is. Maybe it goes where that storage box is?


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## Rick Loncosky (Dec 14, 2002)

Does anyone know about aux. battery holders for 73 -80. I bought one from Mr. Goodwrench, suppose to fit 73 - 87. As you know fenders & hoods changed in 81 and that's what it fits perfectly. I hate to manipulate :crying: a brand new $ 25.00 bracket if there is a perfect fit one available. Any help


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## djd427 (Dec 19, 2004)

Does anyone have any pics of mounting the second battery on the 6.0 gas? I have the factory tray and wiring just needing to pick up 2 new batteries. Want to get the tray all mounted first. Thanks for your help,,,


Hint,,Hint (TLS)


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## DERBYDON (Dec 3, 2004)

*Equalizing charge*

Full time I sell electric forklifts and have learned a thing or three about electric powered equipment - but I'm not school trained.

I think you run an increased risk of ending up with some weaker cells if you don't periodically - say once a month - plug up to a bench charger and overcharge your battery.

What happens with big 18 and 24 cell batteries is that the charger senses a battery is "full" when cells start reaching nominal voltage. But all cells may not be fully charged. Over time they develop a memory and you end up with some weak cells and some strong cells. This is overcome by applying an equalizing charge.

Again, not school trained, but I would think that the same problem can exist with your dual battery setup. Is the voltage regulator connected to both batteries are just the primary.

If I'm going down the wrong street, somebody set me straight.


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## TLS (Jan 31, 2000)

djd427 said:


> Does anyone have any pics of mounting the second battery on the 6.0 gas?
> 
> Hint,,Hint (TLS)


I'm working on it. May go out and buy the batteries today. Wouldn't get a chance to run cables until next week though.

Maybe by the end of the week I'll have a nice pictorial drawn up on the Forums.


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## djd427 (Dec 19, 2004)

Thanks TLS,,, Will wait for you to finish.
Thanks again


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## Bad Luck (Sep 30, 2004)

I'll post some tonight on a 5.3l. Should be the same setup. I bought a stock tray and replaced the stock battery at the same time.


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## VnDrWLawnCare (Jan 27, 2000)

*Bad Luck:--Any pics*

I know this post is nearly a year old, but was checking to see if you have any pics of your dual battery setup. They would be much appreciated.
Thanks
Eric


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## sonjaab (Jul 29, 2001)

Check out these links for full pics aND info:

NBS batt. tray GM#15705102

http://www.gm-trucks.com/forums/index.php?showtopic=43208

http://www.aautodetailing.com/pics/secondbattery/biggerscematicplan.jpg

..........geo


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## TLS (Jan 31, 2000)

All the info you need is in THIS thread.

Go with a direct parallel system. It will save you tons of headaches and give you the power you need WHEN you need it.


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## Detroitdan (Aug 15, 2005)

I have dual batteries in parellel in my truck, factory setup. I constantly had problems with the side post positive terminal that had two cables running to it. It was a special terminal made for both cables, but it always gave me trouble, loosening up and so forth. I eventually removed it and ran a single cable to the side post and the positive from the other battery to the positive top post, so I am utilizing both positive terminals on that battery. I have had one mechanic tell me thats not a good idea, and another says it is fine. I am again having battery issues, I'm going to replace them both this weekend, was wondering if you think it's okay to run them the same way, or if I should try to go back to having the two positive terminals on the same post?


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## TLS (Jan 31, 2000)

I would think either way would be fine. The internal design of a dual post battery has BOTH top and side getting the same GOOD supply.

For side terminals, I use a 3/8" SS bolt and nut.


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## SnoFarmer (Oct 15, 2004)

Detroitdan said:


> I have dual batteries in parellel in my truck, factory setup. I constantly had problems with the side post positive terminal that had two cables running to it. It was a special terminal made for both cables, but it always gave me trouble, loosening up and so forth. I eventually removed it and ran a single cable to the side post and the positive from the other battery to the positive top post, so I am utilizing both positive terminals on that battery. I have had one mechanic tell me thats not a good idea, and another says it is fine. I am again having battery issues, I'm going to replace them both this weekend, was wondering if you think it's okay to run them the same way, or if I should try to go back to having the two positive terminals on the same post?


I recommend getting batteries with both top and side posts. It is much easer to Make your connections and it looks cleaner too. I have used batteries with both top and side posts for over 7yrs with no problems using both sets of terminals at the same time on my dual Battery set ups.


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## mike1316 (Sep 16, 2007)

thanks i am working on mine


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## MAR4CARS (Oct 6, 2005)

I did my dual battery setups with continuous duty solenoids


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## Detroitdan (Aug 15, 2005)

SnoFarmer;269486 said:


> I recommend getting batteries with both top and side posts. It is much easer to Make your connections and it looks cleaner too. I have used batteries with both top and side posts for over 7yrs with no problems using both sets of terminals at the same time on my dual Battery set ups.


Coming up on two years now with no problems. On my pass side one, the positive comes in the top post from the driver side, and the alternator pos connection uses the side post. On the driver side I used the side posts to run the truck, and the top posts for the auxiliary cables that power my plow and sander. So far so good, I'm happy with the setup. Good thing I've got two batteries with dual terminals, or I would have run out of places to hook things up.


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