It would be helpful if you did state model number and coach information.
Is coach gas or diesel? If diesel, is gen diesel or propane?
What does "starter engages-disengages" mean?
Does gen crank over?
If gen cranks over you do not have a battery problem. Check if you are getting fuel. If gas or propane check if you are getting spark.
I have an old Onan gas gen that I use for home backup power. It failed to crank over one time. Turned out that a chunk of carbon had broken loose and blocked the piston. Had to pull heads and clean out the carbon build up.