Power supply device and energy storage system

The invention provides a power supply device and an energy storage system. The power supply apparatus includes a plurality of first battery cells, an equalization circuit, and a heating device. The multiple first battery units are connected in series or in parallel and used for supplying power to external equipment. The equalization circuit is connected between the plurality of first battery units and the heating device; the first battery cell may supply power to the heating device through the equalization circuit such that the heating device heats the first battery cell. When the temperature of the first battery units is lower than a first temperature threshold value, the equalization circuit conducts the first group of battery units in the plurality of first battery units and the heating device to supply power to the heating device. The electric quantity of the first group of battery units is greater than the electric quantity of other battery units except the first group of battery units ...