12V 140A Dual Battery Isolator (VSR)Allows two batteries to be charged from your engine alternator at the same time. When your engine is on and the start battery is sufficiently charged the isolator kit will begin charging the second (auxiliary) battery simultaneously. When the voltage of the start battery drops (i. e.. the engine is stopped) the isolator kit disengages from charging the auxiliary battery. This isolates the start battery and eliminates the possibility of draining it,