2023 Freightliner Issue - PLEASE HELP

2023 Freightliner Cascadia experiencing 13 to 13.6 volts constantly fluctuating at idle and drains to 9 volts instantly when engine is off. Parked for my 34 hour reset Thursday evening and began smelling Sulphur, hopped out and a battery was boiling with smoke spewing out. Took to shop this morning and literally just had batteries checked and one replaced a few hours ago at Love's. Problem isn't fixed...... Thinking alternator because I've been smelling a hot/burning smell after a long day of driving and it wasn't tested today when batteries were. What's weird though, the voltage goes up fine when started, so the alternator must be working right? It just instantly begins dying when turned off. What do y'all think? I'm a lease op so I desperately need help here. Just bought the new battery, was in a freightliner shop twice last week, and I'm getting a new trailer tire in the morning after a puncture. I'm not made of money and dispatch offers crap rates......

 

They were all tested today, one was replaced. I assume that was the one that'd been boiling. No Sulphur smell now, but the voltage problem is still here and now worse. It's honestly scaring me. Don't know whether to keep digging the financial hole I'm in or walk away now.

 

Negative, no inverter. Bare bones truck, no apu, inverter, fridge, pr anything. All I have plugged in is a charger for a cigarette lighter plug to charge tablet and phones.

Truck has 60k miles and was doing great all week. Barely broken in I'd think.

 

Gonna check first thing in the morning and report back to you guys. Hopefully it's nothing too bad or in a ridiculous spot to get to.