For many years battery chargers were simple beasts; a heavy transformer to drop the line voltage and a rectifier to change AC to DC made up the bulk of components. Some added a relay to turn on the charger when the voltage fell. Also, some chargers served as battery boosters with a temporary hit of 50 amps or so to nudge a discharged battery into a start.
These chargers did a lousy job in terms of battery life and fully charging the battery to its potential (pun intended). Both the RV and boating industries were probably the big drivers in the development of sophisticated, computer-chip-controlled, multi-stage chargers, especially for deep cycle batteries.