In standard lead acid battery models, the charger is a fully automatic, constant voltage current limited type. transfer to emergency operation is completely automatic upon failure of utility AC voltage. units are protected against short circuit, reverse polarity conditions and AC lockout. units also have a built-in protection for transformer isolation, surge, transient and low voltage disconnect. emergency operation shall be provided for a minimum of 90 minutes. full battery recharge occurs in compliance with UL 924 specifications. A universal 120/277 VAC, 60Hz input transformer, test switch and long life AC pilot light are all provided standard.