The Dual Battery Isolator Kit Enables Your Accessories to Run From a Separate Battery While the engine is not running on your vehicle While keeping your Main Battery Charged Cut-in voltage: 13.3V Cut-out voltage: 12.8V Instructions 1. When the startup battery voltage is higher than the access voltage, the smart battery isolator (SBI) remains engaged, and the two batteries (startup and house) are charged at the same time. The unit indicator light (LED) is on 2. When the battery is no longer charged from the alternator, the load on the battery begins to delete them. Unit indicator light (LED) is on 3. When the voltage drops below the cutoff voltage for 5 seconds, the SBI will sense it and disconnect it, thus separating the two batteries. Unit indicator (LED) off 4. When the vehicle is restarted, the starting battery has reached the on voltage and the SBI is engaged again. Unit indicator light (LED) is on 5. When the voltage of the starting battery drops, the isolator kit is separated from the charging of the auxiliary battery 6. This isolates the starting battery and eliminates the possibility of running out of battery, ensuring that you always have enough power to start the engine