intheburbs

Nothing really changed from the original writeup. Prices are a little higher, I probably spent closer to $350. I didn't waste too much time shopping around; I bought a lot of the parts this time off Amazon.

25876897 -CABLE; NEGATIVE AUX BAT Qty 1
22783692 -CABLE; POSITIVE AUX BAT Qty 1
25862351 -CABLE; POSITIVE Main to AUX BAT Harness Qty 1
21021808 -NUT – F-Nut, Brass for Mega Fuse Box connections $0.53 each Qty 6
11609411 -NUT – Psngr Air Bag Nut, Stud 1 and aux batt terms $0.38 each Qty 6
12135194 -RELAY; AUX BAT Qty 1
15881616 -COVER; AUX BAT POS JUNCTION BLOCK, F-COVER Qty 1
14005061 -RETAINER; AUX BAT HOLDOWN Qty 1 RockAuto
11509853 -BOLT; AUX BAT HOLDOWN Bolt Qty 1
19116352 -mega fuse holder Qty 1
15305801 -Inline-To Battery Positive Cable Connector – Aux Camper Bat (TP2) Qty 1
13525970 -terminal connectors qty2 (X2 connector, pins B4 and A5)15304711-L Qty 2
12177251 -mega fuse 125 AMP for the aux battery relay Cable MEG125XP Qty 1
278-1223 -45-Ft. UL-Recognized Hookup Wire (18AWG) Qty 1
138212 -M10x1.5x25mm alt ground stud Qty 1

buckley888

I hope this thread is still alive, because this looks like a great solution, but 1 question:

There's a hall effect sensor on the main battery negative cable. It provides feedback on the current draw to a charge controller that will vary the charge voltage based on a number of conditions.

https://www.justanswer.com/chevy/6u8...stem-work.html

Have you had any issues with undercharging since the 2nd battery current would not be detected by the system?

Thanks.

omandave

Hi Buckley,
Welcome to the forums!
I just popped on to look up something else and so I can answer your request based on my experience so far to date... (I installed the TP2 upgrade 8/2013)

it has been four and a half years since the install and I have never had any battery run down or undercharging issues. My batteries are both checked at every oil change as part of the service. they are the same 2 batteries that I installed along with the TP2 option. Both are still running strong. (please know that I may have just jinxed myself by my previous statement! but honesty is worth the risk.) I did install a pair of AGM batteries that I picked up at autozone for a reasonable price (key thing there is look for discount coupons or sign up for the email promotions from a trash email account....)

Hope this helps in your decision to do or not to do. I am glad I did it and I have don't think that it was a waste of money. it allows me to jump start other cars easier too as I now have a slave battery at the front of the vehicle.

CHEERS!!

intheburbs

Bottom line - almost four years with dual batts in the Suburban and almost two years for the Denali, including cold Michigan winters (and cold ungaraged upstate NY winters for the Denali), no issues.

Did some probing with my multimeter on the Suburban. The Denali is 600 miles away. :-(

Voltage with ignition off (measuring off the battery terminals):

primary: 12.26 volts
secondary: 12.83 volts
ostensibly because there are one or more constant-on drains on the primary, and with the ignition off the secondary is electrically isolated.

Ignition on, engine idling
primary: 14.83 volts
secondary: 14.92 volts

Everything looks about right to me, and my enough-knowledge-to-be-dangerous brain.

intheburbs

One additional tidbit of information regarding this setup...

So a few months back, my Suburban starting behaving funny. Using the ignition key I'd just get a "click" and no start. However, remote start worked just fine. I figured it was something like a problem with the ignition switch; I even bought one as a replacement. About that same time, before I started ripping into it, I was talking with my daughter (who's away at college with the Denali) and I told her what the Suburban was doing. She says, "Oh, that means the primary is dead. That's happened to me several times when I've been tailgating with my friends and I drained the primary battery from using the radio for hours."

I was wondering how it would work if the primary was dead. In my case, the battery was at its end of life and I replaced it. Now I know.

wsucougarx

Just bought all the parts to get this installed. Thanks for the write-up!

omandave

So my main agm battery went belly up at Thanksgiving 2020...
so I got 7 years of solid peace of mind on the paired setup.
I replaced both of the batteries with a new pair.
And look forward to another 7 or so years of goodness.
Cheers!

Meller

If this thread is still alive, can the author please explain how this isolates the electronics load from the starting battery? I’ve poured over this information and studied the GMT900 electrical documentation but can’t see how the primary battery positive side opens up when the vehicle is off so that all loads can be carried by the auxiliary battery. Thanks in advance.

omandave

Hi there Meller, and welcome to my original post...
The main relay that is added near the "hood support rod/piston" (12135194 -RELAY; AUX BAT Qty 1) is what does the make/break action of the aux battery.

Part of the installation adds the "running" signal from the fuse panel... Also if you look at the last photo that was posted by "InTheBurbs" there is s secondary relay built into one of the aux harnesses that is also installed.

When the key is in the off position, the batteries are separated.
when my key is turned to the run position, i can here an audible click(clunk) from the main relay, connecting the two batteries positive wires together.
When I turn the key to start, i can audibly hear the main relay disconnect again.
The signal comes from the new pins added to the underside of the fuse block. It adds a positive "sense signal" (power when in "run") that feeds the grey relay to kick the main aux relay to close the batteries together.

When the key is off, or at start position there is no power sent to the inline relay(grey one closer to mega fuse holder)
So the relays are the magic behind the "wire loom"


Hope that helps to explain the real world use of the TP2 add-on for you.

I have zero regrets for installing this into my 2009 suburban.

Cheers and Happy Holidays

Meller

awesome! Thanks for following up! Do you happen to have a sketch showing how the “gray” relay and the X2 connection is wired in? I noticed you have that really cool diagram at the beginning of that write up but there are no additional diagrams to go into the details of that. I tried searching online to see if I could find the documents that contain that diagram but I keep striking out. Do you happen to have the full document that the first diagram in the tp2 write up came from? Thanks again for all of this.