How old are the Batteries?
Sometimes batteries will show a high surface charge,but as soon as you hit them with a load they drop voltage to basically nothing.
I would load test them after being charged after 8 hours.
Or a bad connection.
90 Chev 3500 c/c 4x4,6.2na,400 auto,4:10 gears.DSG Timing gears,main girdle, isspro tach, pyro,boost,oil and trany temp.Dual Tstats, High volume peninsular pump,on shelf, Custom turbo and intercooler 85%complete. Change of plans for the dually, it's going to get a Cummins. Both trucks are Blue 90 4x4 crews