Set up for dual batteries was easy in parallel. I went to Chevy and bought the bracket. Only $26.77 for part # 15246518. The clamp was $7.93 for part 356668. And they did get me for the bolt at $.85. Otherwise real simple. I used one of the bracket mounting points as my ground. As I did not find a good place for a ground on the block or heads on the passenger side. But I did a continuity check and I had an excellent ground. For my hot wire I went to Napa and bought 2 gauge wire. You can buy 4 gauge at Advance Auto or AutoZone, but I figured that much wire I would set up one. I also spent a little more to use the wire loom to keep a factory look.
[attachmentid=10125] old one verses new bracket
[attachmentid=10124]

New bracket goes in very nicely
[attachmentid=10126]

Add second battery
[attachmentid=10127]

Notice the brass fitting where I put my ground wire-- 2 gauge wire
[attachmentid=10128]

Positive ran across firewall
[attachmentid=10129]

another shot of the positive wire coming across
[attachmentid=10130]



simply use your side posts as from factory, and add your positive wire from the second battery
[attachmentid=10131]

This was a simple mod. Double cranking amps and helps her start if I don't run her for a bit. Anyone can do this. The newer chevys already have the tray. All you need to do is get the battery and cable!

Great write up, I wondered if this could be done. Is the second battery the same size (dimensions) as the first one or did you have to get a smaller one?

About the same- I would have to look. It should be said that it is best to run the same batteries for this mod. But in my case my Napa battery is almost new and I came across a deal on the Optima battery. One of my buddies was going to Germany and had to get rid of it. I'll take a new battery for free any day!!

The thing about the second battery is if it would fit in the stock location it will fit in the new one. One thing I didn't care for was the corner bracket can no longer fit as the battery gets in the way.

funny, i was going to make a post asking for those very part numbers. YAHTZEE!

why did you do this mod again?

sorry i didn't check the second post

I did it on mine. I read that the fender brace isn't needed anyway since the bracket braces the fender plenty. I welded up a small mount near the electrical center and put in an isolarot as I'm using my second battery like an Rv house battery.

looks like i found my project for the week. but the only thing is my dad doesnt want me messing with the electrical stuff. i dont know why cause ive done everything from fourwheelers to golf carts to lawn mowers! i guess thats the downside to being 16! haha. im going to put that brace in and set the battery in then take it to a shop and let them hook it up for as cheap as possible!

Parallal isn't all that useful. If you don't run it for a while then your better off buying a battery maintainer than wearing out two batteries for twice the $$.

Eugene makes a good point. Some kind of isolation would be good when the truck's ignition is turned off, but I guess if it's your daily driver, than the chances of a parasitic drain killing both batteries are small.

Chiefa, I hope you don't mind if I add some pics to your pinned thread. You started a good topic.

I did an OEM install. It's essentially almost the same as your install. The batteries come together via the heavy duty solenoid when started, but then separate with the ignition off.

OEM part numbers:

RELAY,AUX.BATTERY 12135194
CABLE,NEGATIVE 15321207
CABLE,POSITIVE;AUX.BATTERY 15372010
CABLE,POSITIVE;AUX.RELAY TO AUX.BATTERY 15372009
CABLE,POSITIVE;STARTER TO AUX.RELAY 15321259
BLOCK,AUX.BATTERY JUNCTION 15305003
FUSE,40 AMP MEGA 15383342
RETAINER,AUX.BATTERY HOLDDOWN 356668
TRAY,AUX.BATTERY 15246518
SCREW, BATTERY 11509853
INSULATOR, BATTERY 10246636
NUT, METRIC BAG OF 10 21021808

Parts Pictured (except the bracket you already posted up):

Some install pics:

You guys building your own hybrids now?

OmarR, that has to be one of the cleanest installs I've ever seen! VERY NICE!

I've always wanted to do that! I bet that thing can't wait to crank up.

Ive been working on an electrical system addtion which includes front and rear power hookups and a duel battery. Here is my relay install location. Its on the Driver Side between the Electrical Box and the firewall. Built a L bracket that floats two relays an inch over the fender to allow parking brake and other stock electrical cables to pass under. Rock Solid!

[attachmentid=10171]
Photo from Fender side - Shows location

[attachmentid=10172]
Photo from Motor side - Shows space undneath

Relay on left goes to duel battery
Relay on right goes to rear of truck

When completed it will be housed in a electrical box and not exposed.

OmarR- thanks for adding more. the more options available the better. Mine works fro me- the isolator will work for others. If you keep things running with the truck off, the isolator is the best way to do it!

Great post, OmarR! I'd like to ask a couple of questions.

First, is the picture of the red cable (with about 5 coils), the part 15372010,
'Cable, Positive, Aux Battery'? Also, in your following post with the pics
of your install, in which pic do I find that red cable?

Second, is the part, "Block, Aux Battery Junction', #15305003, just the fuse holder
for the 40 amp fuse? And, again referring to your pics of the install, what do you
have connected to the LEFT side of the fuse? I see the pigtail from the Aux battery's
postive on the right side of the fuse, but the left hole appears vacant.

You've made such a complicated install so easy to understand, that I'll probably visit
the local GMC dealer and get the parts ASAP. Not being the sharpest pencil in the drawer,
however, I want to make sure I've got it right the first time-- don't really want to
fry myself, or burn my darling to the ground-- ha! She's given me a decade of great
service, and I'd like to get another decade if possible.

Thanks so much for your time, OmarR!

tcoman

Yes, it is just a plastic fuse holder. I currently have nothing connected to the left side.



The thinner red wire that is coiled up about 5 times is part 15372009. I believe this wire is what is supposed to be hooked up to the left side of the fuse holder. In the OEM setup, I believe this wire goes over to the driver side main fuse box, and then you can hook it to the aux power going out to your trailer connection at the rear plug. This way, only your 2nd aux battery will power any electrical needs of whatever you may be towing. (Other than the trailer parking/turn/brake lights)

In my opinion, you don't need this wire. Also, I think it's too thin. If you want to run offroad/aux lights, a winch, etc, off of this mini fuse box going to the 2nd battery, you would install heavier gauge wire going to it anyways.

Also, depending on the OEM SETUP, the relay (solenoid) connects the batteries either thru IGN1 or IGN3. If it was igntion 1, then they both came together to help start the truck. If it was ignition 3, then the 2nd battery was connected in parallel AFTER the truck is running. This is to prevent a run-down aux battery from bogging down the primary battery during startup. IGN3 would be the way to go if you want to power up alot of items while the truck is off.

If your truck did not come from the factory with dual batteries, the solenoid will NOT activate once connected. You will have to make the connection to either IGN1 or IGN3 under the driver's side fuse box. It's really easy, but I will save that for another post.

Any more questions? Ask away...I hope I helped!

May I ask what years these part numbers are for? I have a 2002 Tahoe Z71.

Hey group,

I have a 2008 Tahoe that I would like to add a second battery to. Because I have a lot of high end two-way radio equipment installed, I want to use all OEM parts. The second tray is already in place.

Is there a parts list or "kit" that contains the necessary parts from GM?

Thanks in advance!

Jim

if you just do the parallel way- I did it to a buddys. Neg in the block on the drivers side--right infront of #1cyl. ran postive above the engine on the firewall to the main post. very easy!

isnt there a way you can have a battery selector but will charge both batteries? Under emergency you can use both batteries? I want to do that setup anyone have a schematic or have any experience with that

Sorry i havent been around we have been pretty busy at work

You can use an isolator, a perko switch, or a heavy duty relay....

There are a lot of products that do this. Go look at a Marine store for auto battery isolators. They are made to connect the batteries above a certain voltage to change but disconnect when the supply side voltage drops too low. The usually have a button for emergency linking.

Here are a few.

Starting Isolation (SI) Dual Sensing Automatic Charging Relay

Same as above but with an emergency connect switch - "Add-A-Battery" Dual Circuit System

Smart Charger that controls the charge instead of just bridging the batteries. Would be good for keeping batterys isolated.

Hope that helps. Marine stores have all sorts of battery management systems. You would not believe how complex battery management is on a boat with house, starting, generator, and other battery loads. I used to sail on a boat with a huge battery system and you really need to know how to manage them correctly. Each battery for the house bank was the size of about 4 car batteries combined and we had three of those monsters. Anyway, go down to a marine store and browse. I used to entertain myself for hours in the electrical section.

what no diesel generators?
hha awesome thanks

Ya, we had a diesel generator as well. Post pics of whatever you install.

Def - I will - its going in when the brake controller is - Hauling a 25 fter for snowmobile season wanna make sure shes alll good

wow thats exactly what ive been looking for. the only problem is i have a 145a alternator. and my greengumby if you have a nnbs i believe they have a larger alternator than mine does? not sure but id check on that first

Umm...what?

that kit is only rated for 120 continuous amps...

oh wait..... wooowwww. im a dumbass. fml

deep fried I wanna do the isolater thing on my diesel so that way if one battery drains dead I can still use my other one hopefully. Can you explain a little more in depth please.

If you want to do an emergency jump start system, use any of those isolators with the emergency connect switch. The isolators will kick in when the engine is running to keep the emergency battery charged and if you end up with a dead main battery, just turn on the emergency switch which will connect the emergency battery to the main battery, in essence, a built in jump starter. If you want, instead of an emergency connect switch, you can use a solenoid and mount the remote connect switch inside the truck so you can jump start without opening the hood instead of activating the emergency battery from an engine bay mounted switch. Better for bad weather areas.

New member here... Do you know if the 2008 Suburbans are set up for dual batteries stock? In other words, what mods would I need to do if I want to mod my 2008 Suburban for dual batteries with an isolator. My wife has drained the battery a couple of times and I would like to have a failsafe mechanism in this vehicle for these types of issues.

These work well. I just keep one of these in my trunk. Lot cheaper than dual batteries if all you want is an emergency jumpstart. It also has 12vdc, 120vac, a light, air compressor, inflation, and a bunch of other features. In order to jumpstart you just connect it and it will tell you when its ready and when to crank, no dealing with cables. At least get one of these for jumpstarting other peoples cars. I have never actually used it on my truck, always using it to help other stranded people or get 120v power where power is not available. This thing is great for camping.

Link: http://www.sears.com/shc/s/p_10153_12605_0...rs+%26+Boosters

We also use the truck every summer off-road on the beach. Ideally I would also like to be able to power some AC stuff like a radio, LCD TV, and/or blender... I did a dual-battery setup on my 4runner, but I read somewhere that the Chevy trucks were pre-wired somewhat for dual batteries.

Certain models have kits to install a 2nd battery but the wiring is still up to you. The kits are usually just some metal parts used for holding and bolting the battery down. If you want to use a 2nd battery for an inverter when the engine is off and use it for emergency starting, get a deep cycle/starting battery. I hear that the optomas are good. I believe its the blue top you want.

In the photos previous in the thread, I see that there's some sort of cable that plugs into the OE relay... this is supposed to run to the fuse box to either IGN1 or IGN3... when I looked under the hood of my '05 GMC Yukon Denali, I don't see any plug thats dangling for me to use...

Is one of the part numbers listed to that cable assembly? Or is it supposed to already be there?

Can you quote the thread or give us the post number, if you look at the top if each post, there is a post number. Ex: This post is #40.

Post 12 and Post 13

on the blue seas system add a battery i need a source that is only on during cranking to isolate the batteries. where can i tap into for this? i know its on the started solenoid but how can i find out which wire to use. and please dont tell me to get out that gay voltage meter because i can never get those things to work... haha. shut up i know i should know how to use it but it just wont. i need to get the one with no switches just two wires and a light bulb. haha thatd make it easy!

How do you plan on charging the battery? If you only use it during cranking then it will quickly become discharged. The blue sea systems will automatically connect the battery's once you have started the engine with the main battery. It will connect the 2nd battery and change it so it stays ready. If you are looking for a boost in cranking power when the truck starts, I suppose you could run a solenoid off of an ignition 2 wire that's only on when the key is in the run position. The battery should them be available for cranking and will stay connected when the engine is running to charge. Might not be good though if the 2nd battery is dead since when you goto crank, it will start taking power from the first battery while cranking meaning less power for the starter motor.

Overall, I would think just to stick with the blue sea isolator. If you really need that extra boost, you can activate it manually. Oh, and with the multimeter, the |: symbol is the one you want for measuring DC. No offense but if you cannot get a multimeter working either yours is broken or you should get a friend to do the wiring for you.

hahaha see thats the thing man i understand wiring pretty good now. thats why im going to install this myself. if i had doubts then i wouldnt. but thank you now i know what symbol to put it on. that should come in handy!

i am using the blue seas isolator and i need to find the wire that is live only when cranking because it will automatically isolate the batteries to avoid sending any surges to my accessories connected to my aux. fuse block on the 2nd battery. the wire is optional to install though so i may just skip it. i mean thats what fuses are made for...

if anyone knows of a tutorial of someone installing the blue seas systems add a battery kit i would love to see it. the instructions are just sort of vague and a little confusing. real life pics would be great

What model number did you get? Is there a PDF set of instructions?

You could probably use the wire for the acc power which goes to the radio and other stuff. That power turns off when cranking.

thats why, when i installed my second battery i hooked it up to an isolator and relay, and a pull button switch in the cab. If the main dies, or a want to run music for a long amount of time just pull the switch and the convenience of two batteries.