I missed the SBI12/sbi212, that maybe the missing puzzle to my upcoming wiring nightmare.
As for why to charge my vehicle battery; There is always parasitic drains present in vehicles. If I am going to put an expensive dual/three battery system with solar, I want it to keep my vehicle battery charged (Think extended parking/camping). Further, the Toyota Tundra does not properly charge AGM batteries or Lithium batteries. If I install a system, I want it to top off those batteries so I dont have to hook it up to a charger monthly.
Overland True North has the thought of what I am chasing. The dual battery system under the hood for the stuff I want to add immediately (Winch, lights ETC, ARB AIR). Admittedly I had not considered a product like goal zero to help alleviate a desire for a second battery under the hood. More research, that never seems to end.