That would make it a diesel, I assume? It would be helpful if we knew for sure what chassis and engine you have.My RV is a 2001 National Islander.
There are different batteries for the chassis and for the coach and it would be the coach batteries that supply power to start the generator. For the generator to charge the batteries would take several hours of running but most motorhome generators do not charge the chassis battery anyway.We have run the generator for a bit in hopes it would charge the batteries,
Once you start any engine it will take at least 10 to 20 minutes to replace the charge you take out while starting it. With a diesel, that requires more power so you probably need at least a half hour to recharge and that assumes that your battery is in near new condition. If the battery is getting older or if the electrolyte is low that would mean even longer. The using battery boost means that you were using both the chassis battery and the coach batteries to crank the engine and so you probably now have both discharged. I suggest you use jumper cables to the chassis battery from a running vehicle that has a good battery. Allow it to run for at least 15 minutes connected before you try to start the diesel.Yes, the starter won't crank. I
Since you just bought a motorhome that is now 20 years old, it would be a good idea to remove the batteries and take them somewhere to have them load tested so that you will know their condition. If the seller kept them plugged into electricity all of the time, that was probably because the batteries were old and getting weak and it was the only what to be sure that it would start.