"Get it there" battery charger
"Keep it there" battery maintainer.
You are correct about the disconnect. Unless your MAINTAINER is high amperage an inadvertent load that sucks more power then the maintainer can provide will turn the battery into scrap metal.
Lots of ways to parallel batteries but two maintainers keep stuff separated and plug if one maintainer goes **** up you have a second. If batteries are different construction the charging voltage can be unique by setting a switch.
Trickle charge setting is a work of art. Basically be using DELTA T resistance to maintain float voltage. Gotta drawer full of 750 - 800 ma transformers to play with?