The Smart Battery Isolator, or SBI, allows your auxiliary battery to charge from the alternator while the vehicle is running, and protect the start battery from discharging when the engine is off. It can also be used in-conjunction with an in-vehicle battery charger, or BCDC, to allow the start battery to be jump started from the auxiliary battery in the event that the start battery is discharged or fails.
In a dual battery setup where one battery is used as a starter battery to operate the vehicle and one as a secondary to run electrical devices, the SBI ensures your start battery doesn’t run flat when you use your secondary battery while the engine is turned off. When the engine is turned off, and therefore the alternator is no longer running, the start battery will drop below 12.7 volts and the SBI will disengage the secondary battery. This will stop any loads connected to the auxiliary battery from draining the start battery.