An electric tool, comprising: a housing; a motor, accommodated in the housing; battery pack mounting portions, at least two battery packs (15,151,152) being detachably mounted in the battery pack mounting portions, wherein each of the battery packs (15,151,152) comprises a battery pack housing and a plurality of cells disposed in the battery pack housing; a main switch, being in an open state or a closed state according to an operation of a user, wherein when the main switch is in a closed state, the battery packs (15,151,152) are capable of supplying power to the motor, and when the main switch is in an open state, the battery packs (15,151,152) stop supplying power to the motor; a control assembly, detecting a state of the main switch; and a parameter measurement module, wherein the parameter measurement module is electrically connected to the control assembly, the control assembly obtains state parameters, detected by the parameter measurement module, of the battery packs (15,151,152), and when the state parameters of the battery packs(15,151,152) meet the preset condition and the main switch is in an open state, the control assembly controls transfer of electric energy of a battery pack(151,152) with a high voltage to a battery pack with a low voltage of the at least two battery packs (15,151,152); the preset condition comprises: determining, based on the state parameters, that temperatures of the battery packs (15,151,152) are within a first temperature interval in which mutual charging can be performed; and determining, based on the state parameters, that a voltage difference between the battery packs (15,151,152) is within a first voltage difference interval in which mutual charging can be performed. a housing; a motor, accommodated in the housing; battery pack mounting portions, at least two battery packs (15,151,152) being detachably mounted in the battery pack mounting portions, wherein each of the battery packs (15,151,152) comprises a battery pack housing and a plurality of cells disposed in the battery pack housing; a main switch, being in an open state or a closed state according to an operation of a user, wherein when the main switch is in a closed state, the battery packs (15,151,152) are capable of supplying power to the motor, and when the main switch is in an open state, the battery packs (15,151,152) stop supplying power to the motor; a control assembly, detecting a state of the main switch; and a parameter measurement module, wherein the parameter measurement module is electrically connected to the control assembly, the control assembly obtains state parameters, detected by the parameter measurement module, of the battery packs (15,151,152), and when the state parameters of the battery packs(15,151,152) meet the preset condition and the main switch is in an open state, the control assembly controls transfer of electric energy of a battery pack(151,152) with a high voltage to a battery pack with a low voltage of the at least two battery packs (15,151,152); the preset condition comprises: determining, based on the state parameters, that temperatures of the battery packs (15,151,152) are within a first temperature interval in which mutual charging can be performed; and determining, based on the state parameters, that a voltage difference between the battery packs (15,151,152) is within a first voltage difference interval in which mutual charging can be performed. determining, based on the state parameters, that temperatures of the battery packs (15,151,152) are within a first temperature interval in which mutual charging can be performed; and determining, based on the state parameters, that a voltage difference between the battery packs (15,151,152) is within a first voltage difference interval in which mutual charging can be performed.