A Voltage Sensitive Relay (VSR) works by monitoring the voltage of your vehicle’s main battery and automatically connecting or disconnecting your auxiliary battery based on voltage levels. When the main battery reaches a set voltage (usually around 13.3V), indicating that the alternator is charging, the VSR engages to charge the auxiliary battery. When the voltage drops below a certain point (around 12.8V), the VSR disconnects to prevent draining the starter battery. It’s a simple, hands-off way to manage dual battery systems efficiently.