Victron Smart BatteryProtect 48V-100A
 
The Smart 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.
 
When using Bluetooth to program the Smart BatteryProtect any required engage/disengage levels can be set.

Alternatively, one of nine predefined engage/disengage levels can be set with the programming pin (see manual). 
 
If required, Bluetooth can be disabled.
 
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.