Dual Battery for Factory Accessories

I'm getting ready to do a dual battery setup in my 2020 and would like to do an onboard solution so that I can power factory accessories as well as aftermarket ones. Most of the resources I've found are either ways to charge a second battery while running the truck and isolate it completely while the truck is off -or- a much simpler setup with a solenoid for switching power sources from car audio examples (and boats for that matter). I may be thinking about this wrong or trying to do something that isn't possible or that could be done a better way.

I'd like to have things already attached to the truck powered by a second battery at camp. ie: be able to turn the key to the accessory position and be able to run lighting, coms and even the factory radio and dome lights etc.

Right now I have an aftermarket fuse box as well as a Switch pro running multiple lights. I pulled this from Mike @overland Bound's video and hacked in the accessories on the right.



It's also possible I have this in my head wrong and this is where the factory devices hook in? I don't think this is the case but adding for clarity.




This separates the accessories into 2 groups and does not allow me to run anything wired to the starter. So my question is it possible (by adding a relay or something) or do I need to think about this a different way and rewire the switch pro and aftermarket fusebox directly to the 2nd battery? I don't know if this makes sense or not.

Further complicating this is adding a DC to DC charge manager and solar in the future which I think I can tackle once I figure this isolation out.

Thanks in advance and sorry for the long-winded explanation.

 

If you go with this setup the batteries will be connected most of the time. Make sure you use matched batteries, as the push-pull between mismatched batteries will shorten their lives. This is one reason people isolate the two batteries and run accessories off of a secondary fuse box attached to the aux battery. An isolated setup will also help insure that you have a well charged starting battery after a prolonged period of using accessories that are wired to the aux battery (like a fridge).

 

Yeah doesn't make much sense does it? It's been a few weeks since I posted. I think the solution is to just wire my Switch pro to a 2nd batter under the hood and hook up the DCtoDC etc. Together when on, separate when off. Thanks.