579 wont turn on, no crank, voltage drops as I turn key

579 2016

Woke up this morning, truck turned on fine. Drove for 7 1/2 hours, parked truck, plugged in engine heater. Went home and came back after 2 hours to turn truck on and pick up load. I get a Low Voltage Disconnect warning as Im entering truck

First turn = no crank, hissing/spinning sound (not sure how to exactly describe it) from under hood

2nd turn = hissing/spinning sound, truck turns on

I turn truck off after a minute and try to turn in on again and see if I have the same issue.

Now truck wont even turn on. I have electric power, everything in cab seems to work, but theres no crank, only hissing/spinning sound.

I turn APU on to charge up battery, try to turn it on again and notice as Im holding key to turn on - the battery voltage DROPS down as Im holding key on dash, no crank

Disconnected batteries and left over night and will see what happens tomorrow.


Any ideas? Alternator didnt shut off? (not sure why I got Low Voltage Disconnect, nothing was left on in my truck when I was away 2 hours.

Starter?

Bad batteries? I do keep getting LVD daily, usually if truck is running and I turn APU on, or a few things are running at the same time

Inverter has some play in this?

 

Replaced starter, now good