The Victron Solid Switch 104 is a small and super handy switch, especially useful to control an alternator, for example, a Balmar or Master Volt Alpha-Pro, in a Victron lithium system. The Solid Switch is wired in between the Allow-to-charge (ATC) contact from a BMS and the ignition. Its main advantage, over for example a relay, is the incredibly low power draw: 0.04 Ah per month, versus 21 Ah monthly of a typical 12V 1 Amp relay.