Incase of Mains failure, the output
is connected to the Battery. The Battery Voltage is monitored by
additional circuitry, which prevents deep discharge of the Battery.
The Power Supply can also
be safely operated without connecting a Battery, in case Battery backup
is not required. The circuitry is protected against damage due to
Battery Reversal, Output short-circuit, and Dead Battery Charging. An
array of LEDs indicate the status of the system. http://www.zeebeetronics.com/12v_3A_SMPS.html