Energy storage system and power supply method thereof

The embodiment of the invention discloses an energy storage system and a power supply method thereof. The energy storage system comprises a power supply device for supplying power to a direct-current bus, and a main battery and a standby battery which are connected to the direct-current bus in parallel, and the power supply method comprises the steps that when the power supply device works normally, the power supply device supplies power to a load, the power supply device carries out floating charging on the standby battery, and the main battery is in a standby mode; when the power supply device is powered off, the standby battery supplies power to the load, and meanwhile, the main battery is triggered to be switched from the standby mode to the standby power mode to start to supply power to the load; when the output power of the main battery is balanced with the power of the load, the output power of the standby battery is zero, and the standby battery is in a bypass state; and when the maximum output power