Aux Battery For 2011 Gmc Sierra 1500 Sle

[guitarcoach]

Recently I posted about how I wanted to install an auxiliary battery in my new Sierra.

 

I wanted a second battery to be able to use an inverter for charging laptops, etc., to run my little Mobicool cooler, plus other accessories while on an upcoming camping trip.

 

It looked like I was going to have to pay big $$$ to do this project, upgrading my truck to the TP2 option, or using a smart battery isolator system. However, after much research and conflicting guidance, the tech at my local RV dealership came up with a simple, inexpensive way for me to get what I needed.

 

He noticed that my truck came with the trailering equipment option. After properly grounding the new deep cycle aux battery, he ran a wire from the trailer power connection at my fuse panel to the battery's positive terminal, so charging would be supplied via that connection. He then hooked up (to that same positive terminal) the already-supplied red/black trailer power wire, which runs to the round 7 connector at the rear of my truck.

 

This way the truck "thinks" it has a trailer battery connected, although it's under the hood!

 

I can now connect up my inverter to the aux battery if/when I need it, and also run my cooler in the back of the truck while parked or driving using a nifty round-7-to-dual-cigarette-lighter-plug adapter.

 

I popped into my GM dealer and showed the install to their electronics guy, and he approved the method. Apparently this hookup keeps the two batteries isolated from one another.

 

Total cost to me (less battery): about $60 CAD.

 

Thanks to everyone who pitched in with suggestions!

 

Matthew

 

[ChevyTech77]

I'm not sure if I agree with charging a deep cycle battery like we do a normal battery plus you're going to pull power from both of the batteries, not just the one you added, with it wired in that manor. You still have to have an isolator if you don't want to pull power from the truck's normal battery. I would have used a more substantial wire/connector combo as well but that's just me.

[[email protected]]

I don't understand what your saying, the way you said it sounds like either it's isolated all the time or it's never isolated and is allowed to run your main battery down also, in other words what do you do to isolate it when you want to and then hook it back up so it can charge. And I hope you used fuses and you should've used bigger wire.

[guitarcoach]

Man, oh man, this is getting confusing. I've had so many different points of view offered. I don't know which one to trust!

 

This method I've gone with is what the head tech at a real big RV place in my city recommended, plus the go-to guy for electronics from my GM dealer approved the set up. Both guys were aware of the deep-cycle battery, and the GM guy expressed no concerns about wire gauge, either.

 

Just when I thought I was out, they pull me back in. Sigh.

 

More comments would sure be welcome. I have to pull this together before the 20th of this month.

 

Thanks in advance...

 

Matthew

[old-chevy-dude]

well I bought the Painless Performance Dual Battery Digital Power Manager (http://www.painlessperformance.com/webcata...archField=40120), 2 Yellow Top Optima Deep Cycles, Wired it all up in under 2 hours and it has been good to go for several months, no issue.

 

 

I even killed the second battery listening to the radio and watching the rear tv while camping and the truck started no problem and the aux battery was charged by the time we got home from a 400 mile drive.

 

the Painless has a indicator light that tells you which battery is being charged, and we tested it when we got home and it was good to go.

 

 

Painless was $160 and the 2 batteries were $320..

[ChevyTech77]

Man, oh man, this is getting confusing. I've had so many different points of view offered. I don't know which one to trust!

 

This method I've gone with is what the head tech at a real big RV place in my city recommended, plus the go-to guy for electronics from my GM dealer approved the set up. Both guys were aware of the deep-cycle battery, and the GM guy expressed no concerns about wire gauge, either.

 

Just when I thought I was out, they pull me back in. Sigh.

 

More comments would sure be welcome. I have to pull this together before the 20th of this month.

 

Thanks in advance...

 

Matthew

I stand by my previous post. Your current install is nothing more than a second battery added in parallel, for the most part. The two local techs that you're dealing with are in need of some further electrical schooling sorry but that's the truth. I can guarantee you that if you hook an electrical device to your trailer connector on that truck, you will drain both batteries NOT just the added one. As for the wire/connector comments, it appears as though you used 10ga cable with regular crimp on terminals. Considering the electrical load that can be pulled from a battery, you could burn those up in no time flat. Take that all for what it is worth but again, I stand by my previous post.

[[email protected]]

Agreed, and be careful if your main battery goes weak and you try to start the truck it can catch those lil bitty wires on fire. Looks like 12 gauge to me.

[guitarcoach]

Thanks for your responses. I'm getting the impression that you guys just may be right about this.

 

Last night on my drive home from work I noticed my truck making a whining noise. When I pulled over and turned off the ignition the sound continued for a second or two, winding down kind of like when you take your finger off the trigger of an electric drill. The noise started up again when I restarted the truck - I popped the hood, but could not determine the source of the whine.

 

I had to drive home, and the noise gradually went away. However, I noticed that my dashboard battery gauge was reading lower than normal. It's usually pinned at a hair over 14V, but now, if it were a gas gauge I'd have just a 1/3 of a tank.

 

Can't wait to start it up this morning, see what else goes wrong. If it does start, I'm heading straight to the dealer. If they determine that these problems are due to this aux battery hookup I'll then head straight to the RV place and have them remove their work.

 

What a drag.

 

Matthew

[guitarcoach]

...and now my "Check Engine Light" is steadily on as I drove to work today.

[ChevyTech77]

Generator issues now, I'll bet. That sucks dude but that's why doing modifications can always come back to bite you and usually saving a buck or two in the process, will cost you much more in the long run. Hopefully, you get this stuff jerked off your truck before it burns to the ground.

 

Your charge gauge will always vary on a newer GM vehicle as the generator is turned on and off, as demand is needed, by the ecm and bcm. If you add a second battery wired in parellel and the generator gets confused, can't keep up or overworks itself, guess what? You have the issue you currently have.

 

Again, that sucks dude but electrical systems on todays newer vehicles especially, are nothing to screw around with. Just pull the wires off the aux battery, add the Painless Wiring isolator, and move on. Hopefully your GM dealer will work with you a bit on the generator but in all honesty, they are going to be lying to GM about it to get it covered under warranty so they really don't have to cover anything.

[dwhitton]

I dont think a drained main battery will draw from the Trailer side of things since the main feed back to the 7 pin is 12 guage only (if that). Im sure GM isolated the trailer feed from the starting circuit in the event that you did have the trailer hooked up during a restart on a dead main battery so you wouldn't over draw on such a small guage circuit.

 

This set up still won't supply to start with a dead main, but you will have double amp hour capacity for your trailer when hooked to the 7 pin only. My 2 cents. Make sure hook up is Parallel (neg to neg / pos to pos) to your trailer circuit or you will toast your trailer wiring with 24 Volts.

 

I would be concerned on the alternator also, after a big drain on the spare battery, the alternator wourlbe working overtime (14.5+ charging volts) to keep up with charging. A heavy duty alternator would be considered.

 

I find that my alternator fights to keep up with my trailer battery after some time of "off grid" camping, so much so that at low idle (stop light with A/C on), the alternator will "drop off" to take a break, voltmeter dropping to 12.7 volts (read electrical system on pure main battery)

 

I just isolate the main when parked for long times with a ground disconnect, the green nob battery post type. I tried the "red key" type located in the engine compartment but after a year the heat made the switch fail (with the nasty issue of an intermittent ground)

 

I know the security is disabled, but it will take them a while to find out why the thing wont start, and the only thing I have to do if when I reconnect is to reset the time on the clock. Way better then waiting an hour for a boost. (FYI, I also have a protable booster under the rear seat incase it does go dead $100)

[ChevyTech77]

The post his aux battery is connected to is a fused, full battery supplied post so it is not isolated from the vehicle's first battery, or remaining electrical system, at all. I could well in fact backfeed, for sure, under the right circumstances. Again, just another reason that battery isolators are made.

[dwhitton]

Like I say, the trailer circuit should be isolated from the starting curcuit in the event that your main goes dead and you try to start while the trailer is hooked up through the 7 pin.

 

The wires you see in the pictures are the stock guage GM supplies in the Trailer package harness. The posts you see are for trailer supply to 12V 7 pin and brake controller feeds. They just matched the same guage for the ground.

 

Im saying that the purpose of the 12V feed in the trailer circuit is for charging your trailer battery only, or running low current 12V supply to small appliances. In no way was that circuit intended to be used to supply the current required to start a dead vehicle, otherwise the 7pin 12V circuit wire, hooked to a trailer battery, being over 20 ft away, would need a 1 guage wire as a minimum to supply the required current over that distance.

[guitarcoach]

Like I say, the trailer circuit should be isolated from the starting curcuit in the event that your main goes dead and you try to start while the trailer is hooked up through the 7 pin.

 

The wires you see in the pictures are the stock guage GM supplies in the Trailer package harness. The posts you see are for trailer supply to 12V 7 pin and brake controller feeds. They just matched the same guage for the ground.

 

Im saying that the purpose of the 12V feed in the trailer circuit is for charging your trailer battery only, or running low current 12V supply to small appliances. In no way was that circuit intended to be used to supply the current required to start a dead vehicle, otherwise the 7pin 12V circuit wire, hooked to a trailer battery, being over 20 ft away, would need a 1 guage wire as a minimum to supply the required current over that distance.

 

Don, are you approving this method of hooking things up? The aux battery is a deep-cycle, and I simply want to be able to throw my 12V cooler in the cargo bed and keep it running during my upcoming trip. I may also use an inverter to power a little fan for in our tent. Other than that, not much else...charging laptop and phones, I guess.

 

Your comments are appreciated. All of you!

[kdixer]

Thanks for your responses. I'm getting the impression that you guys just may be right about this.

 

Last night on my drive home from work I noticed my truck making a whining noise. When I pulled over and turned off the ignition the sound continued for a second or two, winding down kind of like when you take your finger off the trigger of an electric drill. The noise started up again when I restarted the truck - I popped the hood, but could not determine the source of the whine.

 

I had to drive home, and the noise gradually went away. However, I noticed that my dashboard battery gauge was reading lower than normal. It's usually pinned at a hair over 14V, but now, if it were a gas gauge I'd have just a 1/3 of a tank.

 

Can't wait to start it up this morning, see what else goes wrong. If it does start, I'm heading straight to the dealer. If they determine that these problems are due to this aux battery hookup I'll then head straight to the RV place and have them remove their work.

 

What a drag.

 

Matthew

 

The following is from page 4-79 in my 2009 Silverado owners manual:

 

*The fuses for these two circuits are installed in the

 

 

 

underhood electrical center, but the wires are not

 

 

 

connected. They should be connected by your

 

 

 

dealer/retailer or a qualified service center. The fuse

 

 

 

and wire for the ITBC is factory installed and connected

 

 

 

if the vehicle is equipped with an ITBC. The fuse for

 

 

 

the battery feed is not required if the vehicle has

 

 

 

an auxiliary battery. If the vehicle does not have an

 

 

 

auxiliary battery, have your dealer/retailer or authorized

 

 

 

service center install the required fuse.

 

 

 

If charging a remote (non-vehicle) battery, press the

 

 

 

tow/haul mode button located at the end of the

 

 

 

shift lever. This will boost the vehicle system voltage

 

 

 

and properly charge the battery. If the trailer is too light

 

 

 

for tow/haul mode, turn on the headlamps as a

 

 

 

second way to boost the vehicle system and charge

 

 

the battery.

 

If the battery is hooked to the correct terminal at the fuse panel, it is fused in the fuse block. When people hook up the connector that comes from the factory taped to the wiring beneath the brake booster, a fuse has to be added to the fuse block to get power to the 7 pin connector at the hitch. I am in agreement that this setup should be "safe" as far as a fire hazard. But I am not sure that this circuit is isolated in a way that it cannot drain your other battery. I suspect the circuit is isolated in a vehicle start event but that is it.