An electrolyte refilling system for a battery pack comprising: a plurality of battery cells each comprising a cell accommodating case configured to accommodate the electrode assembly comprising a negative electrode plate, a positive electrode plate, and a separator interposed between the negative electrode plate and the positive electrode plate, wherein the cell accommodating case has, on one side thereof, a cell filling port comprising a filling valve, and has, on the other side thereof facing the cell filling port, a cell discharge port comprising a discharge valve; a battery pack in which the cell filling port of each battery cell is connected in parallel to each other through a main filling tube, the cell discharge port of each battery cell is connected in parallel to each other through a main discharge tube, the cell filling ports and the cell discharge ports are accommodated in an outer case, and a main filling port of the main filling tube and a main discharge port of the main discharge tube pass through the outer case and are exposed to the outside; a liquid filling pump connected to the main filling port of the main filling tube of the battery pack; a solvent tank comprising a solvent valve configured to supply or block the solvent supplied to the liquid filling pump; an electrolyte tank comprising an electrolyte valve configured to supply or block the electrolyte supplied to the liquid filling pump; an electrolyte refilling determining unit configured to calculate a 1C capacity holding rate (%) of the battery pack and determine the necessity of refilling the electrolyte; a supply amount calculating unit configured to calculate amounts of the solvent and electrolyte to be supplied to the solvent tank and the electrolyte tank; a control unit configured to control, according to the determination of the necessity of refilling the electrolyte from the electrolyte refilling determining unit, the filling valve, the discharge valve, the liquid filling pump, the solvent valve, and the electrolyte valve so as to supply the calculated amounts of solvent and electrolyte to each battery cell constituting the battery pack; and a notifying unit configured to notify a user of the necessity of refilling the electrolyte and the calculated amounts of solvent and electrolyte, wherein the 1C capacity holding rate (%) is calculated by Equation 1 below: 1 C capacity holding rate % = Current 1 C discharge capacity Initial 1 C discharge capacity × 100 in Equation 1, the initial 1C discharge capacity is a discharge capacity calculated when the battery pack has been manufactured, and the current 1C discharge capacity is a discharge capacity of the battery pack in use. a plurality of battery cells each comprising a cell accommodating case configured to accommodate the electrode assembly comprising a negative electrode plate, a positive electrode plate, and a separator interposed between the negative electrode plate and the positive electrode plate, wherein the cell accommodating case has, on one side thereof, a cell filling port comprising a filling valve, and has, on the other side thereof facing the cell filling port, a cell discharge port comprising a discharge valve; a battery pack in which the cell filling port of each battery cell is connected in parallel to each other through a main filling tube, the cell discharge port of each battery cell is connected in parallel to each other through a main discharge tube, the cell filling ports and the cell discharge ports are accommodated in an outer case, and a main filling port of the main filling tube and a main discharge port of the main discharge tube pass through the outer case and are exposed to the outside; a liquid filling pump connected to the main filling port of the main filling tube of the battery pack; a solvent tank comprising a solvent valve configured to supply or block the solvent supplied to the liquid filling pump; an electrolyte tank comprising an electrolyte valve configured to supply or block the electrolyte supplied to the liquid filling pump; an electrolyte refilling determining unit configured to calculate a 1C capacity holding rate (%) of the battery pack and determine the necessity of refilling the electrolyte; a supply amount calculating unit configured to calculate amounts of the solvent and electrolyte to be supplied to the solvent tank and the electrolyte tank; a control unit configured to control, according to the determination of the necessity of refilling the electrolyte from the electrolyte refilling determining unit, the filling valve, the discharge valve, the liquid filling pump, the solvent valve, and the electrolyte valve so as to supply the calculated amounts of solvent and electrolyte to each battery cell constituting the battery pack; and a notifying unit configured to notify a user of the necessity of refilling the electrolyte and the calculated amounts of solvent and electrolyte, wherein the 1C capacity holding rate (%) is calculated by Equation 1 below: 1 C capacity holding rate % = Current 1 C discharge capacity Initial 1 C discharge capacity × 100 in Equation 1, the initial 1C discharge capacity is a discharge capacity calculated when the battery pack has been manufactured, and the current 1C discharge capacity is a discharge capacity of the battery pack in use.