A system for preventing overvoltage of a battery in which two or more cells are provided, the system comprising: a voltage measurement unit configured to measure a voltage of each cell in a preset period interval; a first control unit configured to compare a first measurement voltage value of at least one cell measured by the voltage measurement unit with a prescribed first reference voltage value, determine the at least one cell as being overvoltage when the first measurement voltage value is equal to or greater than the prescribed first reference voltage value, and output a cutoff signal for cutting an inflow of a charge current when for the at least one cell its first measurement voltage value is equal to or greater than the prescribed first reference voltage value; a cutoff unit configured to receive the cutoff signal from the first control unit to cut off the inflow of the charge current to the battery cells; a cell balancing unit configured to compare a voltage difference between the cells to perform cell balancing; and a second control unit; characterized in that the cell balancing unit comprises a balancing Field Effect Transistor, FET, and a balancing resistor, the balancing FET is configured to be on/off-controlled according to a control signal from the second control unit, and in the balancing resistor a cell current is discharged by the balancing FET being turned on; wherein the system further comprises: the second control unit comprising a voltage comparison unit and an overvoltage determination unit, wherein: the voltage comparison unit is configured, for the at least one cell which has been determined to be overvoltage by the first control unit, to compare a second measurement voltage value of the at least one cell measured by the voltage measurement unit in a next period interval with a prescribed second reference voltage value determining the at least one cell as being overvoltage, and the overvoltage determination unit is configured to output a turn-on signal to the balancing FET of the cell balancing unit to discharge the at least one cell when the second measurement voltage value is equal to or greater than the prescribed second reference voltage value according to a comparison result of the voltage comparison unit. a voltage measurement unit configured to measure a voltage of each cell in a preset period interval; a first control unit configured to compare a first measurement voltage value of at least one cell measured by the voltage measurement unit with a prescribed first reference voltage value, determine the at least one cell as being overvoltage when the first measurement voltage value is equal to or greater than the prescribed first reference voltage value, and output a cutoff signal for cutting an inflow of a charge current when for the at least one cell its first measurement voltage value is equal to or greater than the prescribed first reference voltage value; a cutoff unit configured to receive the cutoff signal from the first control unit to cut off the inflow of the charge current to the battery cells; a cell balancing unit configured to compare a voltage difference between the cells to perform cell balancing; and a second control unit; characterized in that the cell balancing unit comprises a balancing Field Effect Transistor, FET, and a balancing resistor, the balancing FET is configured to be on/off-controlled according to a control signal from the second control unit, and in the balancing resistor a cell current is discharged by the balancing FET being turned on; wherein the system further comprises: the second control unit comprising a voltage comparison unit and an overvoltage determination unit, wherein: the voltage comparison unit is configured, for the at least one cell which has been determined to be overvoltage by the first control unit, to compare a second measurement voltage value of the at least one cell measured by the voltage measurement unit in a next period interval with a prescribed second reference voltage value determining the at least one cell as being overvoltage, and the overvoltage determination unit is configured to output a turn-on signal to the balancing FET of the cell balancing unit to discharge the at least one cell when the second measurement voltage value is equal to or greater than the prescribed second reference voltage value according to a comparison result of the voltage comparison unit. the voltage comparison unit is configured, for the at least one cell which has been determined to be overvoltage by the first control unit, to compare a second measurement voltage value of the at least one cell measured by the voltage measurement unit in a next period interval with a prescribed second reference voltage value determining the at least one cell as being overvoltage, and the overvoltage determination unit is configured to output a turn-on signal to the balancing FET of the cell balancing unit to discharge the at least one cell when the second measurement voltage value is equal to or greater than the prescribed second reference voltage value according to a comparison result of the voltage comparison unit.