Auxiliary Battery Setup

parshal · August 8, 2009

I have an '09 1500 Sierra with the 145-amp alternator, the power pack plus package and integrated brake controller. A friend of mine is a mechanic at a nearby Chevy dealer and I had my truck in there this morning to have the brakes looked at. He noticed the wiring the topper installer had done at the battery and said I should relocate it to the fuse box. There are two connection points there, one where the brake controller is powered and another "spare". He put a 30-amp fuse in and showed me where to connect it. Through the conversation we started talking about the spare battery tray that's installed. I had a 3 port 12-volt outlet installed in the topper that runs off the battery that I use to run a fan for my dog box. He said I could add a second battery and it could power the outlets so it wouldn't drain my main battery. I've read a bit on this site about the various options but most discussions are about older trucks and mention buying the tray which mine already has. In any case, I was wondering if anyone knew if there was a factory kit (rather than aftermarket) and had the part numbers. I can only seem to find a link in a few threads to a Wrangler site.

Essentially, I'd like to be able to power the outlets in the back of the truck off the auxiliary battery and have it charge from the alternator but remain isolated when the truck is off. That's what my friend described and it sounds like the TP2 option from some of these threads.

C. Charles Hahn · August 9, 2009

The only way I've found so far indicates using an aftermarket isolator for this; if there IS a factory isolator I'd love to hear about it too! For now I'm just going to wire up a second battery in parallel and double the reserve capacity. As long as accessories aren't left on full time there shouldn't be any problems as a result.

montecarlo31 · August 13, 2009

15942731-CABLE;NEGATIVE AUX BAT

15942730-CABLE;POSITIVE AUX BAT

25862351-CABLE;POSITIVE AUX BAT RH

21021808-NUT (QTY 2)

11517293-NUT (QTY 2)

12135194-RELAY;AUX BAT

15881616-COVER;AUX BAT POS JUNCTION BLOCK

14005061-RETAINER;AUX BAT HOLDOWN

11509853-BOLT;AUX BAT HOLDOWN

parshal · August 19, 2009

Thanks for the part numbers! I assume they are good for the '09's.

The first one, however, doesn't come up as a valid part number on http://www.gmpartsdirect.com.

terryk · August 19, 2009

http://www.rv.net/forum/index.cfm/fuseacti...id/23024768.cfm

That's for the 99-2007 but I would assume the basics are the same.

parshal · August 19, 2009

I did a search and found online that 25876897 replaces 15942731.

2COR517 · August 19, 2009

The factory "isolator" is a relay. Monte gave you all the numbers, but you can probably go cheaper at Napa/Autozone. A snowplow pump is a perfect relay. For your usage, you only need a #10 charge wire.

parshal · August 20, 2009

Can anyone tell me if this setup will automatically have the trailer tow power come from the aux battery or will it need something else?

H&H sent me a diagram of the TP2 setup and it shows the relay mounting to the firewall below and left of the master cylinder with two studs. I don't have studs on my firewall in that location. Will I need to drill the firewall to add them? Or, does this mount somewhere else?

2COR517 · August 20, 2009

On my 97, the trailer batt wire is connected to the main fuse block. I would switch it over if I did any drycamping.

parshal · August 31, 2009

The parts should arrive tomorrow so I've been doing a bit more research. In answer to my question above about the trailer power coming from the aux battery I found this post

http://www.gm-trucks.com/forums/index.php?...st&p=600726

which suggests that the aux battery is connected to the same post on the underhood electrical center as the trailer power wire. Note the important note after step 4 where it says devices powered by this fuse will drain the vehicle battery if left connected with the vehicle not running. I'm assumed this is the starting battery and not the auxiliary battery. However, if the fuse is not installed, there is no power to that post (assuming no aux battery). When the fuse is installed it has power from the main battery. So, if the fuse is removed and the aux battery is installed it should be pulling from the aux battery unless the key is on.

Does anyone know how the aux battery is charged? Does it come through the battery cables or the post on the underhood electrical center?

jeeperman · August 31, 2009

I know this has been mentioned before, but I have to put a plug in for Wrangler Power Products: http://www.wranglernw.com/.

I have their dual battery setup in both of my Jeeps. I love being able to have the control from inside the cab to switch between isolated batteries, or placing them in parallel. When the vehicle is off, the batteries are isolated so that one can't drain the other. When the vehicle is running, both batteries are being charged. If you want/need, you can flip the switch from inside the vehicle to put the batteries in parallel. This can be done for winching, or if you need to jump the starting battery.

I'll say it now - they're not cheap. With the GMT-900 at least you won't need the auxiliary battery tray.

This setup has saved my butt more than once while out in the woods. The piece of mind of being able to jump-start the main battery all by myself is definitely worth the added expense.

Scott

parshal · September 2, 2009

Well, I got the main harness installed along the firewall and it has two connectors on each end. One connects to the relay and the other, by the main battery, well, I don't know where that connects. I'm assuming it's there to send voltage to relay when the key is turned but I can't figure out where it connects. Until I get that figured out I'm not adding the battery cables.

Also, I assume I have to drill two holes for the relay since I can't find existing studs to attach it to.

Anybody have any ideas? I've attached pictures.