Low current drain

This 24V low voltage disconnect unit is a low power device which protects batteries from damage and helps extend battery life.  A 12V version is also available.

They have a factory default disconnect voltage of 21.6V or 10.8V respectively and are said to be easy to set up with an adjustable power supply. The three state of charge LEDs automatically adjust when on load so you can see remaining battery capacity at a glance.