Using a separate power supply for charging an RV battery bank may be cheaper - especially if you already own one - but of course using them takes more messing around whenever you charge the RV batteries. Hit and run RV'ing is not too compatible with messing around. Permanently squatting in a spot for weeks on end with time on one's hands may be another deal, however"
That's it in a nutshell. Having the luxury of even one overnight a week with a power pedestal changes the whole battery maintenance ballgame, pitcher, dugout and outhouse...
Some folks shun RV ghetto jamming where someone flushes the toilet and everyone in a four rig radius hears it. The last thing I want to hear when I exit holding a cup of coffee is, "Golly, you're up awful early today".
Boondock City. It's worth extra battery work in my case.
But press a button and endure 12 hours to charge the batteries on generator power isn't my bag. I want to get it over and done with and go fishing, lay in a hammock or -anything- rather than listen to a generator pickpocket my wallet...