I would bet first your battery is discharged, but an original univolt that old should not be trusted.
I would check the voltage, then plug in to shore power, and check the voltage again. That will be quick checks of the battery and the univolt.
"Those who expect to reap the blessings of freedom, like men, must undergo the fatigue of supporting it." Thomas Paine
'08 34' Classic SO, '12 Ram 2500 4X4, 6.7L Cummins.