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...
