Whenever the AC input power dips or fails, input power to the inverter shall be
automatically supplied from the batteries without interruption. When the AC power is
restored, input power for recharging the batteries shall automatically be supplied
from the charger. If the main input power does not return, the UPS shall
automatically shut itself down when the battery plant reaches its discharge limit.
When the UPS shuts down, it shall transfer its load to the alternative power source,
if this is available, or terminate the supply if it is not.