An energy storage unit comprising: a battery string, wherein the battery string comprises a plurality of battery cells; a plurality of balancing units, wherein the plurality of balancing units are configured to control state of charge balance between the battery cells, and the plurality of balancing units are in a one-to-one correspondence with the plurality of battery cells, each battery cell is connected in parallel to an input end of a balancing unit corresponding to the battery cell, output ends of the plurality of balancing units are connected in parallel, characterized in that positive output ends of the plurality of balancing units are connected to a positive balancing bus of the energy storage unit, negative output ends of the plurality of balancing units are connected to a negative balancing bus of the energy storage unit; a voltage conversion unit configured to perform voltage conversion, wherein a positive input end of the voltage conversion unit is connected to a positive electrode of the battery string by using a battery bus of the energy storage unit, and a negative input end and a negative output end of the voltage conversion unit are grounded; a first switch, having a first end connected to the positive electrode of the battery string by using the battery bus and a second end connected to the positive input end of the voltage conversion unit; a second switch, having a first end connected to the positive balancing bus and a second end connected to the positive input end of the voltage conversion unit; and a control unit configured to: control the first switch to be closed and the second switch to be open, to enable the voltage conversion unit to receive a voltage by using the battery bus; or control the first switch to be open and the second switch to be closed, to enable the voltage conversion unit to receive a voltage by using the positive balancing bus. a battery string, wherein the battery string comprises a plurality of battery cells; a plurality of balancing units, wherein the plurality of balancing units are configured to control state of charge balance between the battery cells, and the plurality of balancing units are in a one-to-one correspondence with the plurality of battery cells, each battery cell is connected in parallel to an input end of a balancing unit corresponding to the battery cell, output ends of the plurality of balancing units are connected in parallel, characterized in that positive output ends of the plurality of balancing units are connected to a positive balancing bus of the energy storage unit, negative output ends of the plurality of balancing units are connected to a negative balancing bus of the energy storage unit; a voltage conversion unit configured to perform voltage conversion, wherein a positive input end of the voltage conversion unit is connected to a positive electrode of the battery string by using a battery bus of the energy storage unit, and a negative input end and a negative output end of the voltage conversion unit are grounded; a first switch, having a first end connected to the positive electrode of the battery string by using the battery bus and a second end connected to the positive input end of the voltage conversion unit; a second switch, having a first end connected to the positive balancing bus and a second end connected to the positive input end of the voltage conversion unit; and a control unit configured to: control the first switch to be closed and the second switch to be open, to enable the voltage conversion unit to receive a voltage by using the battery bus; or control the first switch to be open and the second switch to be closed, to enable the voltage conversion unit to receive a voltage by using the positive balancing bus.