Smart Alternator
An alternator type that changes its output voltage on the instruction of the engine control unit, cutting back charging from time to time while driving in order to save fuel. Because it does not hold the voltage constant, it cannot reliably charge a directly connected service battery.
A conventional alternator holds its output at around 14 V. In a smart alternator the engine control unit monitors the state of charge of the starter battery and the driving condition and varies the voltage: it raises it during braking and can lower it to a value such as 12.5 V at constant speed to save fuel.
From the service battery's point of view this behaviour is problematic. In a system using a split charge relay or a direct connection, charging stops when the voltage drops; the relay may even fall below its cut-off threshold and switch on and off continuously. As a result, at the end of the journey the service battery is charged far less than expected.
The solution is to build the connection between them not with a voltage-sensing relay but with a DC-DC charger that holds its output steady even when the input voltage drops. On new model tow vehicles and motorhome chassis this approach has become standard. If you plan to recover loads such as the levelling system, the refrigerator and the inverter while driving, first verify which type your alternator is.
The context in which this term is used: RV automatic levelling guide