The red rotary switch with 1, 2, Both and Off is still the most common battery switch on boats. Position 1 or 2 connects one bank to the boat, Both parallels them, and Off isolates them. It carries the full starting and charging current.
Rod Collins of Compass Marine argues the switch itself is fine and the trouble is how it's wired and used. On most builder installations the alternator charges through the switch, so turning it to Off with the engine running opens the charging path.
What a surveyor checks
Look behind the switch at the studs and cables for heat discolouration, loose nuts and hard insulation. Then Compass Marine's flicker test: cabin lights on, turn the switch slowly from 1 through Both to 2. Good switches are make-before-break; if the lights flicker, the switch has worn and should be replaced. Note how the alternator is wired, and whether the owner knows not to switch off with the engine running.
In the report
"Battery switch, 1-2-Both-Off, lights flicker when switched between positions, heat discolouration on the common stud. Alternator charges through the switch. Replace the switch and label it not to be turned off with the engine running." See battery switch.