Victron Energy Argo FET 100-2 battery isolator allows simultaneous charging of multiple batteries without connecting them together. This means that if you were to discharge one battery then it will not affect any other batteries, such as the starter battery. Usually adding a split charger will result in a big loss of voltage, however the voltage drop in Victron Argo FET isolators is less than 0.02 Volts at low current and only around 0.1 Volts at higher currents.

Some alternators require DC voltage on the B+ output to provide charge to the batteries and usually a diode or FET splitter will stop any voltage returning to the alternator, however this Argo FET isolator will give a special limited input to power the B+ when the engine run / stop switch is closed.