This is most commonly a loose connection or poor battery charging.
Step 1 use multimedia to check battery voltage if over 12.5 (which is quite discharged) it should still turnover
Step 2 If voltage good, but not turning over, check hot battery connection. Use wire brush on positive terminal (be careful) and reset terminals ideally covering in petroleum Kelly
Step 3 If voltage low, re-charge or if stuck, you should have a solenoid in glove box to join coach and auto battery. Otherwise, you can join starter and coach via jump leads, but only use in emergencies
Mostly, it is poor connections
Think outside the box