Set the voltage where you would like the load (van 12v) to disconnect, this will pretect your battery from discharging too low and extend the life expectancy.
There are 4 pre-set voltages to choose from and the disconnect/connect takes place automatically.
It has a on/off switch to turn the protection on or off. allowing any 12 volt loads to continue using battery power with or without this protection.
 
FEATURES
• Stop batteries from being over discharged.
• Switches load on/off automatically 
• Optional remote on/off feature
• Can also operate as a master switch for 12V circuits
• Used by many caravan OEMs