ECM? ECU?

I was driving my 2016 Peterbilt 389 today and noticed my check engine light was faintly lit...but everything was running good.
Tonight I had a headlamp warning pop up about 120miles from home. Then things started getting weird.
I let off the throttle to pass through a small highway town and my highlights dimmed and brightened as I braked and accelerated. Then I turned on my signal light and the headlight were blinking off and on with the signal.
At this point, I was about 50 miles from home so I figured get it home and check it out in the morning. Truck was running good.
About 15 miles later...my lights are getting dimmer and dimmer...until I have no headlights at all. I turned the headlights off and the daytime running lights were still working. About 10-15 miles later...they also stopped. Luckily I was just pulling into a town about 20 miles from home.
I pulled into a dark service road and tried to pull straight as I could without lights.
Pulled the brake and set the high idle.
Ran for about 15 minutes and the red stop sign pops up on the dash and shuts me down.
I managed to hook up InSite and got a code SPN 3597 FMI 2
Waited for a bit and I was able to start it again...but it only ran for about 2 minutes and did the same thing.
Now it won't restart, is giving me Tractor ABS fault and says to check fuses for chassis node. I check them under the hood and they were all good.
And now it also won't let me hook up InSite...give me communication error.
Of course it's pitch black outside...and I'm trying to work with a flashlight...but I can't see anything that looks like a problem at the chassis node or ECM.
Truck just turns over but won't fire to start up.
Stuck in a small town at 130am Saturday night. Good times

 

I took a look at the gauge when the lights were dimming and it was charging at 14v and the ampmeter was almost zero...so I figured the alternator was charging.

 

So morning came and I called a guy to come try to boost me. We hooked up power to one battery and ground to battery on far side...waited for a bit and wouldn't clear ABS and wouldn't start. Then we hooked both live and ground to battery closest to engine and heard some clicks at the engine. Turned the key and it fired up.
He left and about 20 seconds later it emergency shutdown engine again with ABS/chassis node faults.
The batteries were installed March 2021 but I bought 4 and changed them anyway....and was able to get home 20 miles to my place.
Also bought an alternator and will do some checking at shop when I get home

 

Thanks. I definitely check that out tonight in the shop. I didn't have the room to bring the old batteries home today...but I'll be picking them up on Tues and testing them as well.