DUAL SUPPLY OF A BACKUP POWER SUPPLY

A power backup system includes a multi phased energy storage and a backup supply. The energy storage includes battery strings, each capable of supplying either an AC or DC voltage to a load. During normal operation, the backup supply is configured for being supplied with an AC voltage from a utility grid and being connectable to a DC voltage supplying battery string of the energy storage. During abnormal operation, the backup supply is configured for, in a first period of time, being supplied from a DC output voltage established by the a first battery string and after expiration of the first period of time being supplied from the AC output voltage established by a second battery string.