The BatteryProtect disconnects the battery from non-essential loads before it is completely discharged (which would damage the battery) or before it has insufficient power left to crank the engine.

The Battery Protect is a uni-directional device. It can only deal with current in one direction, so either current to a load, or current from a charger, but not both currents at the same time. In addition to this, current only can flow from the Battery terminal to the Load terminal. In case of use with a load, the battery connects to the Battery terminal, and in case of use with a charger, the charger connects to the Battery terminal.