Batteyr charging in an RV

Has anyone here ever come across a manufacturer claiming their converter is capable of internally isolating external loads, when, in fact, it wasn't?

i don't know IF they ever claimed it
but the old Magtechs isolated the battery..they would supply approx 30amps to the house and trickle charge the battery with 6amps
i converted several of them to use the house voltage as "battery charging"
making them a parallel system instead of an isolated system
only useful for dry campers to help charge the batteries faster
these people had been running a generator all day to charge the batteries
and the batteries would not carry the heater all night
because it was not charged..6amps just did NOT cut it
at least one of those campers later bought a B&D 40amp that he is still using, 5 years later