A power battery assembly, comprising: a battery circuit having a plurality of battery modules connected in series and/or in parallel; a circuit protecting unit connected in series with the battery circuit and having a relay and a current sensing unit connected in series with the battery circuit, with the current sensing unit detecting a value of a current passing through the relay; characterised in that the circuit protecting unit also has a switching unit connected with the relay for controlling the relay; and a controller connected with the switching unit and the current sensing unit, the switching unit comprising a first MOSFET and a second MOSFET connected in series, with grid electrodes thereof being connected with output terminals (41, 42) of the controller respectively, the controller controlling the switching on or off of the switching unit based on comparison of the value of the current detected by the current sensing unit with a first predetermined current value and with a second predetermined current value, and if the current has a value larger than the first predetermined current value and lasts for a first predetermined time period, the switching unit is switched off in that the first MOSFET is switched off under the control of the controller, so that the relay is switched off; and the switching unit is switched off in that the second MOSFET is switched off under the control of the controller if the current detected by the current sensing unit has a value larger than a second predetermined current value larger than the first predetermined current value and lasts for a second predetermined time period. a battery circuit having a plurality of battery modules connected in series and/or in parallel; a circuit protecting unit connected in series with the battery circuit and having a relay and a current sensing unit connected in series with the battery circuit, with the current sensing unit detecting a value of a current passing through the relay; characterised in that the circuit protecting unit also has a switching unit connected with the relay for controlling the relay; and a controller connected with the switching unit and the current sensing unit, the switching unit comprising a first MOSFET and a second MOSFET connected in series, with grid electrodes thereof being connected with output terminals (41, 42) of the controller respectively, the controller controlling the switching on or off of the switching unit based on comparison of the value of the current detected by the current sensing unit with a first predetermined current value and with a second predetermined current value, and if the current has a value larger than the first predetermined current value and lasts for a first predetermined time period, the switching unit is switched off in that the first MOSFET is switched off under the control of the controller, so that the relay is switched off; and the switching unit is switched off in that the second MOSFET is switched off under the control of the controller if the current detected by the current sensing unit has a value larger than a second predetermined current value larger than the first predetermined current value and lasts for a second predetermined time period.