2nd battery install in a GMT900 Suburban - TP2 option

CampingN.C. wrote:

A friend of mine bought a dually 8.1 new in 2001, I went with him to pick it up, it had two batteries, no special order.
However, I just looked at a 2006 for sale and it only had one, so who knows. Maybe they only did it in the early years. I was just stating that it's possible and that GM has at some point done it on the 3500's that had 8.1's

It just depends on the option package ordered.

GM offered a dual battery OPTION in all the years of the 8.1 GMT800, from 2001 thru 2006. Not every dealer checked that box. Not every buyer knew there was such a box to check.

There are about a half dozen different RPO codes for dual batteries. The OP executed the TP2, which is the most popular for gas vehicles, and the one recommended by GM upfitter advisors for retrofitting. Yet there are a some dual battery RPOs for gas engine GMT800s that do not have isolation during ignition off, like TP2 does.

In the GMT800 series, some of the Special Service (Govt, Police) dual battery RPO's were paralleled full time, similar to the diesel trucks. And then in others, they were isolated, but instead of the second battery feeding the trailer battery feed circuit, it fed a separate mini load center for mobile communication equipment.

Rather than inventory all of the different factory battery wiring options for the GMT800, let's instead focus on the best choice for RV'rs, like Burbman and the OP, and look only at TP2.

Burbman, a second battery can be added to your Burb without interfering with your A/C lines at all. However, I would COVER those A/C lines, because they are aluminum, highly conductive, travel horizontally very near to and along the same path as the positive and negative terminals of the secondary battery, and will go POOF if both terminals end up contacting the A/C line simultaneously when dropping the battery in or pulling it out, or if inadvertently messing with the side terminals.

Here is a TP2 retrofit installation on a 2005 Suburban. This one in the photos below also used all GM parts and factory relay and wiring, yet it is unique, in that the curved fender to firewall brace is retained, even with a full size Group 34/78 battery...

intheburbs wrote:
The GMT800 trucks come with the battery in the front drivers side of the engine bay. I also have a 2001 Suburban 1500, so I'm aware of this. The aux battery goes on the passenger side, behind the wheel well, tucked up against the firewall. Remove the curved brace that connects the fender to the firewall/cowl, and the second battery drops right in.

The GMT900 trucks are the opposite - they come with the battery in the passenger side up against the firewall. The aux battery goes in the front drivers side of the engine bay. That's all I was saying about the difference between the platforms.

NOW I understand...when you said "opposite" I was thinking passenger side behind the grill and driver's side by the firewall. Thanks for clarifying :)

intheburbs wrote:

CampingN.C. wrote:
The 3500's that had the 8.1's came stock with two batts, there's room.

Not the 8.1L trucks, the diesels came with two batteries.

Just a point of clarification - I'm borderline OCD.

The GMT800 trucks come with the battery in the front drivers side of the engine bay. I also have a 2001 Suburban 1500, so I'm aware of this. The aux battery goes on the passenger side, behind the wheel well, tucked up against the firewall. Remove the curved brace that connects the fender to the firewall/cowl, and the second battery drops right in.

The GMT900 trucks are the opposite - they come with the battery in the passenger side up against the firewall. The aux battery goes in the front drivers side of the engine bay. That's all I was saying about the difference between the platforms.

A friend of mine bought a dually 8.1 new in 2001, I went with him to pick it up, it had two batteries, no special order.
However, I just looked at a 2006 for sale and it only had one, so who knows. Maybe they only did it in the early years. I was just stating that it's possible and that GM has at some point done it on the 3500's that had 8.1's

CampingN.C. wrote:
The 3500's that had the 8.1's came stock with two batts, there's room.

Not the 8.1L trucks, the diesels came with two batteries.

Just a point of clarification - I'm borderline OCD.

The GMT800 trucks come with the battery in the front drivers side of the engine bay. I also have a 2001 Suburban 1500, so I'm aware of this. The aux battery goes on the passenger side, behind the wheel well, tucked up against the firewall. Remove the curved brace that connects the fender to the firewall/cowl, and the second battery drops right in.

The GMT900 trucks are the opposite - they come with the battery in the passenger side up against the firewall. The aux battery goes in the front drivers side of the engine bay. That's all I was saying about the difference between the platforms.

Thanks NC I will have to investigate further!

BurbMan wrote:

intheburbs wrote:
You do. Same goes for the GMT800 platform, except the reverse: your primary battery is in the front drivers side location, and the aux battery location is the passenger side against the firewall.

X2

That's not reversed then that's the same config as in your picture above. My a/c components are much more to the right. There's not a lot of extra room under the hood with the 8.1 in there. I will have to do some digging!

The 3500's that had the 8.1's came stock with two batts, there's room.

I know what it's supposed to look like because a friend is the chief of police and he let me look under the hood of his Tahoe.

I also wanted the ability to isolate a battery to make sure I was never stuck in the backcountry somewhere with dead batteries. I also wanted something that was turnkey/automatic. I have to do nothing extra to protect/isolate the aux battery.

Seems pretty pointless to drop in a second battery and not be able to isolate one.

When I dropped a second battery into my Yukon, I just ran a ground to the alternator mounting bolt, and a positive to the alternator 12v stud. Unless you know what it *should* look like, the only thing you notice is the lack of the covers on the cables on the new battery.

intheburbs wrote:
You do. Same goes for the GMT800 platform, except the reverse: your primary battery is in the front drivers side location, and the aux battery location is the passenger side against the firewall.

That's not reversed then that's the same config as in your picture above. My a/c components are much more to the right. There's not a lot of extra room under the hood with the 8.1 in there. I will have to do some digging!

BurbMan wrote:
Nicely done! Wish I had room for a 2nd battery in mine!

You do. Same goes for the GMT800 platform, except the reverse: your primary battery is in the front drivers side location, and the aux battery location is the passenger side against the firewall.

There are similar writeups for that platform. Here's one

rjxj wrote:
Nice job. You may want to watch the depth of discharge with it not being deep cycle. Or are they both deep/marine type batteries?

They're both DieHard Gold Advanced AGM batteries. They can take some serious abuse. Platinum is not available in this size. They have a 36-month replacement warranty, so if I kill 1 or 2 I'll switch to deep cycle.