# Adding a second battery '15 GMC



## Motorman 007 (Jan 11, 2005)

I'm going to put a second battery in my new '15 GMC 2500HD. There is already a battery tray and hold down installed in the truck from the factory. My question is...I have the camper provision already wired in the truck with the termination coiled up on top of the fuel tank. Is this already wired into the truck or are there terminations under the hood somewhere that I need to connect? 
I've read the dual battery sticky. Do most of you just connect the batts together using one or two gauge cable or do you isiolate them?


----------



## dieselss (Jan 3, 2008)

What does the wires on top of the fuel tank have to do with dual batteries?


----------



## Motorman 007 (Jan 11, 2005)

dieselss;1842520 said:


> What does the wires on top of the fuel tank have to do with dual batteries?


It doesn't really... other than in my previous trucks some of the wiring including the trailer brakes and 12V feed weren't connected from the factory and if I needed to do that, I would connect it to the second battery.

Did you have something constructive to add???


----------



## dieselss (Jan 3, 2008)

Yes Francis I do 
Pos to.Pos neg to frame, engine block, accessory bracket, or other stout piece of metal. When making your end it's always better to use copper ends and to solder them. Proper heat shrink tubing as well covering well past the end of the eyelet.
When attaching the gnd to the "place of contact" wire wheel or scrape off any paint or undercoating that is there. I personally like to put a dab of dielectric grease where I cleaned down to bare metal due to the rust factor.
Not sure what your positive battery clamp looks like but you may have to buy a new one or attach the 2nd batt cable elsewhere. In which case a pic would be needed 
Usually an isolator isn't necessary, and 2g cable should be sufficient


----------



## calhoun (Oct 18, 2003)

If you use your camper for rustic camping (no hookups) I would isolate. You can then run your fridge, lights, sounds, etc off the battery and still have a fresh one to start the truck with in the AM. I have a 2500watt inverter hooked to my isolated battery I then plug in the camper as if I do have hookups without the generator noise.
For plowing just hookem together.


----------



## snowymassbowtie (Sep 22, 2013)

*If you connect*

the batteries direc to each other they should be as close as possible in age size etc. Even if the truck is new the battery could be 6 mos. old. The best way to add a second battery would be to run the second battery positive to a constant duty solenoid powered by key power and then your ground as mentioned above. If the batteries are not the same one will destroy the other


----------



## dieselss (Jan 3, 2008)

What's the point of the solenoid when going batt to batt?


----------



## Whiffyspark (Dec 23, 2009)

I would just buy the harness and hold down from the dealer. You dropped 40k what's a couple hundred lol


----------



## Motorman 007 (Jan 11, 2005)

Whiffyspark;1845389 said:


> I would just buy the harness and hold down from the dealer. You dropped 40k what's a couple hundred lol


I dropped a whole lot more than $40K on this beast.....The battery tray and hold down are already in the truck. I just need the cables. Thanks


----------



## snowymassbowtie (Sep 22, 2013)

What's the point of the solenoid when going batt to batt?
Your not connecting batteries directly. they are wired thru the solenoid.


----------



## dieselss (Jan 3, 2008)

So what's the point of it? That's my question?


----------



## SnoFarmer (Oct 15, 2004)

"Adding the duel batteries connected directly together and upgrading the stock charging wire and ground cables will allow the system to operate at peak efficiency and allow the alternator to provide all the amperage it can to keep the batteries charged."

and
When your at idle your alt is putting out less then what is required to run all of your lights, ACC;s and lifting your plow, a 2nd batt will help your lights to stay bright and lessen the load put on the single batt.

There are more reasons but I'm running low on ink.


----------



## dieselss (Jan 3, 2008)

Mass, was saying to add a solenoid to the 2nd battery. My question was. What is adding a solenoid going to.Do? And why?


----------



## calhoun (Oct 18, 2003)

Adding a solonoid isolates the 2 when truck is not running. You can run one totally down and still have the other to start. See my comment above. It all depends on what use you need the 2nd battery for.


----------



## dieselss (Jan 3, 2008)

Still do not see the need in a plow application


----------



## calhoun (Oct 18, 2003)

No need to isolate if plowing is why you are installing the 2nd battery. The OP mentioned camper wiring. If camping is why he is installing a 2nd battery then this wiring, connected to an isolated battery, is a good way to go.


----------



## Motorman 007 (Jan 11, 2005)

calhoun;1850455 said:


> No need to isolate if plowing is why you are installing the 2nd battery. The OP mentioned camper wiring. If camping is why he is installing a 2nd battery then this wiring, connected to an isolated battery, is a good way to go.


Thank you....


----------



## snowymassbowtie (Sep 22, 2013)

The solenoid is added to keep the batteries isolated from each other when the vehicle is not running. When the vehicle is off the 2 batteries try to equal out,meaning the bad will suck life from the good. So if you do wire them direct thats what happens and also why if you do go direct they should be the same age,size etc.. This was how we wired ambulances, as well an option we offered to plow trucks and any other type of vehicles we wired. If you have 2 identical (or close as possible) batteries you dont need it. But like Calhoun said it will work as a back up if your primary was dead.


----------



## Cosmic Charlie (Feb 1, 2009)

I just noticed that on the new 2015 2500 HD's there is NO option for ordering DUAL batteries (?) like my 2011 has ...


----------



## cat320 (Aug 25, 2000)

Cosmic Charlie;1854653 said:


> I just noticed that on the new 2015 2500 HD's there is NO option for ordering DUAL batteries (?) like my 2011 has ...


the option is there it will cost you $135 730 CCA


----------



## Cosmic Charlie (Feb 1, 2009)

cat320;1854764 said:


> the option is there it will cost you $135 730 CCA


I assumed it was just a larger battery ... no clear it's a 2nd one


----------



## cat320 (Aug 25, 2000)

Cosmic Charlie;1854938 said:


> I assumed it was just a larger battery ... no clear it's a 2nd one


When you are on the build it part you can click on that part for more info and it says it is an aux battery.


----------



## George C (Aug 24, 2004)

Guys,
I just had a stereo system installed in my truck. Two amps, and I think the system can pull up to 40 amps. 
The system went into "protect" and shut down when I was using my XLS for the first time. The stereo system draws directly from the battery. I'm guessing there isn't enough power to remain stable under a quick load spirt. 

Possibly a dual battery setup may offer more available voltage and protection?
Anyone have a differing idea to solve my problem?
Thanks.


----------



## Whiffyspark (Dec 23, 2009)

George C;2078125 said:


> Guys,
> I just had a stereo system installed in my truck. Two amps, and I think the system can pull up to 40 amps.
> The system went into "protect" and shut down when I was using my XLS for the first time. The stereo system draws directly from the battery. I'm guessing there isn't enough power to remain stable under a quick load spirt.
> 
> ...


Mean green alt and another battery


----------



## Motorman 007 (Jan 11, 2005)

George C;2078125 said:


> Guys,
> I just had a stereo system installed in my truck. Two amps, and I think the system can pull up to 40 amps.
> The system went into "protect" and shut down when I was using my XLS for the first time. The stereo system draws directly from the battery. I'm guessing there isn't enough power to remain stable under a quick load spirt.
> 
> ...


I'm gonna bet that you have the same problem many of us have with our 2015 GMs with a plow. This thread is very long but it sounds like you need the "fix" that is supposedly available now from GM

http://www.plowsite.com/showthread.php?t=161166


----------



## George C (Aug 24, 2004)

Thank you for the link, and pointing me in the right direction.
Yes, that sums up my issue. My dealer is starting the process.


----------



## Motorman 007 (Jan 11, 2005)

George C;2078351 said:


> Thank you for the link, and pointing me in the right direction.
> Yes, that sums up my issue. My dealer is starting the process.


Did your dealer have any knowledge of the issue? Mine doesn't and I'm waiting for this supposed letter that is coming out mentioned in the other thread.


----------



## George C (Aug 24, 2004)

No, my dealer did not.
The service manager is the kind of guy you want. He's smart and gets on it.
He called me back to tell me that there isn't a fix at this point, but will have more answers after he talks to his reps.

The problem doesn't seem to be battery. It's an overload of volts from the plow package alternator that is kicking everything out. His info is telling him that before the fix is distributed, we should run everything we can that uses power in the truck while plowing. Wipers, seat heaters, fans, everything to take up voltage so the spike softens before kicking everything out.

I'm trying to get him ask and see if GM will toss in a second battery for free, and give another place for the volts to dissipate.
We'll see how that goes..


----------



## cat320 (Aug 25, 2000)

George C;2078391 said:


> No, my dealer did not.
> The service manager is the kind of guy you want. He's smart and gets on it.
> He called me back to tell me that there isn't a fix at this point, but will have more answers after he talks to his reps.
> 
> ...


I would lover to have the second battery as well on GM to do it before it was penuts but to add it after the fact it cost almost $1k
did you register your truck with Nate from GM ? I guess he will send out info when they have enough to dist to dealers.


----------



## Whiffyspark (Dec 23, 2009)

Maybe a capacitor would help? Not sure of what kind of sound system you put In. Caps are usually for under voltage spikes though


----------



## George C (Aug 24, 2004)

cat320;2078491 said:


> I would lover to have the second battery as well on GM to do it before it was penuts but to add it after the fact it cost almost $1k
> did you register your truck with Nate from GM ? I guess he will send out info when they have enough to dist to dealers.


My dealer quoted me around $600 to do the job. 
I had my service mgr call, but he got a recording. Hopefully, I'll have more info this week.


----------



## George C (Aug 24, 2004)

Whiffyspark;2078492 said:


> Maybe a capacitor would help? Not sure of what kind of sound system you put In. Caps are usually for under voltage spikes though


Yeah, the problem is the other way. Spike.
The system is a Memphis car audio. Six speakers, two subs, and two separate amps running the system.


----------



## Whiffyspark (Dec 23, 2009)

I'm pretty sure you can buy the gm parts and install a 2nd battery way cheaper than $1000. Last harness I replaced was in the $200 range


----------



## GA73 (Feb 6, 2006)

just put dual batteries in my 2014. 2 brand new dekka agm's and cable cost me $345 
very simple diy
my chevy dealer told me they don't even use the gm harness


----------

