The Smart BatteryProtect 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 only flow from the IN terminal to the OUT terminal. In case of use with a load, the battery connects to the IN terminal, and in case of use with a charger, the charger connects to the IN terminal.