sentences:  This is beneficial because a weak or dead battery will drain the charge from a strong battery if both are connected directly together.The disadvantage to an isolator is added cost and complexity, and if a diode-type isolator is used (which is very common) there is additional voltage drop in the circuit between the charging source and the batteries.Battery isolators are commonly used on recreational vehicles, boats, utility vehicles, airplanes, and large trucks where one battery is dedicated to starting and running the engine and another battery or batteries run accessory loads (e.g., winches, radar, instruments, etc.