This device is designed for charging the battery of a semi-trailer when the towing vehicle’s cables are connected. The BCU-300 prolongs the life of the semi-trailer battery and prevents it from being fully discharged. The device automatically recharges the battery if the semi-trailer has been parked for a long time, or if it has been transporting non-refrigerated products for a long time. The device will charge your semi-trailer’s battery without the need for any additional wires or devices, just by connecting the tractor’s wires.