Enerdrive 140A 12/24v Voltage Sensitive Relay (VSR)When the engine is started, starting and auxiliary batteries are separated allowing only the starting battery to be charged. When the charge voltage reaches 13. 2 volts the VSR engages allowing both starting and auxiliary batteries to be charged. When the engine is stopped and the battery voltage falls below 12. 8 volts the VSR disengages separating the start and auxiliary batteries. The auxiliary battery continues to power any accessories without