This circuit can protect your battery to avoid a to low discharge. In this example the voltage source is the battery and the lamps are the load. When the voltage drops below 10 volts, this circuit cuts off the power supply for the load. The threshold can be influenced by the chosen Zener-diode and the potentiometer.
In alternative, you can use this circuit for an overvoltage protection by connecting the load at the other output of the relay.
