Has anyone dealt with this

Is your metal bar in tact , The one that holds your batteries down

 

Any rubbed or raw spots on batt. cables from batt. to starter will make that happen also look at each hold down on batt. cables for wear?

 

Peterbilt has a quick disconnect for the ECM above the starter. Maybe loose or corroded. Not sure if Volvo is the same.

 

It could be a sensor,see if any dash arrows flicker just before power loss.

 

I have deal with this.
Disconnect power cable from the battery and check
all lengths. From battery under cab on the frame all the way to the front firewall. Run your fingers around the wire to check any scuffs on wire insulation. If truck is equipped with quick disconnect switch take it out and clean terminals.
On my ex (I'm sooo happy now) truck wire had 3 shorts. One to the frame right where wires leaving battery box and two between positive and negative under the cab front/fender. I know it's a PITA.
The other place to check cab front firewall deep under air tubes and wire harness two connectors for power.
The best in the world Volvo engineers didn't expect we have rain and snow here so water is draining directly on electrical connectors. Make sure it tight and clean

 

Years ago I had a 2006 Volvo company ride just up and die while driving on a busy 2 lane highway.... yeah.... luckily I got it pulled into a wide driveway. It was running fine and then everything died, no power, no motor running, no nothing... Tow truck came and got me. The next day they found the culprit to be badly corroded connections to a fuse that was inside the battery box. I believe this wire and fuse ran directly from the battery to the ECM. They fixed it and I was on my way. This was a common issue I was told. I seem to recall there were tell tale electrical graemlins before the big break down. This was about 8 years ago. But all anyone back at the shop could do was just scratch their heads.