Should batteries be disconnected when on shore power?

I believe this whole idea of disconnecting batteries is in deed coming from memories of yesteryears fixed voltages converters, that really would over charge batteries in hot weather.
To the OP, if you have a 9200 series converter, you do not have to check the water once a month, or even twice a month, probably not even 3-4 months, trust me ! To be safe, try every 4-6 months for 12v batteries, even longer for 6v. But in reality, you'll probably give them a little water once a year.