True story: When I was growing up you could let a Diesel engine idle all day but try that with a Gasoline engine and you'd foul the plugs.
Today.. Well it is basically the reverse. A diesel at full idle for long periods may fail emissions test but you can idle a computer controlled Gasser all day.
(Source: Click and Clack the tappet brothers. or Car Talk on PBS long ago)
The moral: Things change
Back long ago there was a fantastic device a converter charger made by a company called Magnetek, model series 6300 and if you left your batteries connected it would fry them if plugged in too long... That is no longer made
Nearest thing to it today is the Parallex (they bought 'em out) 7300 and it should not do that.
Most RV's today have either a Parallex 7300 Or equivlent OR a good 3 stage converter like.. Well the best is the Progressive Dynamics wizard controlled units or their equal Some are even programmable .
These .. Well I leave my batteries turned on 99.99 percent of the time (Turn off when refilling propane tank Turn back on a few minutes later) and the batteries last 7-9 years.