Product Description: Sea-Dog 4227901 Smart Dual Battery Isolator, 12V This Smart Dual Battery Isolator is ideal for dual battery applications. Allows two batteries to automatically charge at the same time and then isolates the batteries, ensuring the starting battery is always charged and ready for use. Automatically engages or disengages the circuit at pre-set voltages by sensing the input voltage generated, eliminating the possibility of discharging the primary starting battery. Cut-in voltage: 13.3V. Cut-out voltage: 12.8V. Surge protected. Features an LED indicator to alert the user when the unit is engaged. Constructed of machined brass with a weatherproof injection molded nylon housing and durable silver tipped contacts. Installs with two #8 RH fasteners (included). IP65 rating.