2016 Peterbilt 388 Pride and Class

I have a LVD/CECU issue. So far, checked batteries, fuses, mega fuse, it all started after using the APU I believe, coincidence? Maybe. Also, dome lights, door lights, some outlets now off, don't work. Sometimes I get the truck won't start issue, turn the APU on, truck starts up. Last 8 of my VIN# is GD353569
I don't know where the LVD is and if it's CECU controlled and location of the CECU. Not sure we checked the ground, we did read the cab doesn't have a ground to the frame, it's all grounded through the ECM/CECU, so a rogue GPS, CB, Samsara ground to the cab can cause this as well? Any help moving forward is greatly appreciated.
So many stories of this same issue on so many trucks on here. I can't find many that finish this issue. I'd rather not jump it, I want to know what's wrong, so any suggestions, ill try it, post results, and keep going until I can figure it out and post pictures, with hopefully the results to help others.
Thank you all for any help moving forward

 

Thank you for reaching out and asking the questions I should have added in the original post. The batteries were put in at the end of 2022, these interstate batteries are a couple months old. Also they were just pulled, load tested by 3 different shops. One being the interstate dealer this morning, as this battery was the lowest reading of the 4 of them and he said it's fine, although a little low. All fuses, wires, batteries, alternator were checked by the same mechanic. He said he'd have to dig into it, wasn't sure exactly what it was.

Never, not once has the truck thrown the LVD code or screen. The only thing this truck ever did that would make us think LVD was an audible alarm, while the truck was off, ignition on, I checked remotely, no codes, and voltage read 13.5 volts, turned the key off, alarm kept going for about a minute and turned off. Turned the key and it started up like nothing was wrong. Voltage will drop to 12, I caught it going down to 11.5 on samsara when we had the alarm. When you drive the truck, stop for a break, or just turn it off, when you go to start it sometimes the problem arises. The voltage inside the cab, and remote through samsara shows always above 13.5 volts. Turn the key, truck goes through startup procedure, gauges, lights all check out, turn the key, nothing, no crank, no click, nothing. Like the batteries were disconnected. Wait a minute, or more, starts right up. Again, never have we seen a LVD light or code.
Thanks again for your insight, anything else you need to try to figure this out I'll happily get.
Thanks