I am having strange electrical issue with my 2017 4runner. I am running a redarc dual battery system that has worked with zero issues for over 4 years. I had to replace the main battery a few months ago under warranty and everything was working fine until my Spod would not turn on with the 2nd battery. The 2nd battery tested fine, but I changed the battery and the Spod works fine.
a month later the 4runner died again when I was out. Nothing on the dash was lighting up or door activation. I checked the battery connection and everything looked visually ok. I was able to jump the + from the dual battery and start the the 4runner. When I put it in reverse the car died again.
Once again I jumped the battery and it started.

When I was driving home I could not control the passenger or rear windows from the door buttons but I was able to control my window and the rear window from the rear door.(issue fixed) I have no clue if this is different issues or all related.

The shop I use is 60 miles away and hard to get appointments, or I can take it to Toyota for a diagnostics. I am not sure about more local shops with all the upgraded wiring.

when 4runner is running, I am getting 13.5 V on meter so not sure if the alternator has issue? looking into sdhq offroad upgraded alternator?

you're probably not going to like this but I think the way forward here is to return to stock battery setup and reassess. if everything seems to be working fine then it's the dual battery setup. I don't think it's the Spod but perhaps something is internally malfunctioning with the dual battery set up

taking to toyota they are going to either 1) blame the dual battery set up or 2) make you remove the dual battery set up before doing further diagnostics

the 5th gen alternator should put out just under 14v when engine running. 2017 seems a bit new for an alternator issue already. hunch is your dual battery set up is causing the gremlins

It's easy enough to disconnect the wire to the Redarc dual battery system and test the system. the main battery is a type 31, It's been working fine for 4 years. it's been hit and miss when the 4runner goes down. the 4runner only has 40,000 miles.

The main battery only has a winch and the dual battery. All the other upgrades run on the 2nd battery.