A method of manufacturing a battery pack having a plurality of assembled batteries (10-1 to 10-X) connected in parallel, each of the assembled batteries (10-1 to 10-X) including a plurality of cells, the battery pack being configured to let an allowable circulating current flow through the assembled batteries, the method comprising: a) determining a number (Mi) of the cells connected in parallel and a number (Ni) of the cells connected in series in each of the assembled batteries (10-1 to 10-X) based on the following conditions to, Ii = Voi − Vo 1 + β − β ∧ 2 − 4 αγ ∧ 0.5 × R 1 2 α Ri α = R 1 ∧ 2 × ∑ 1 Ri β = − R 1 × Vo 1 × ∑ 1 Ri − ∑ Voi Ri − Vo 1 × ∑ 1 Ri γ = W − Vo 1 × ∑ Voi Ri − Voi × ∑ 1 Ri SOCi t + Δ t = SOCi t − Ii t × Δ t 3600 × 100 CAPi × Mi × μi Ik = − ∑ Ii i = 1 ∼ k − 1, k + 1 ∼ x where: indexes 1, i and k represent the corresponding assembled battery (10-1 to 10-X), I represents a current of the corresponding assembled battery (10-1 to 10-X), Vo represents an open circuit voltage of the corresponding assembled battery (10-1 to 10-X) and depends on the number of cells connected in series in the corresponding assembled battery (10-1 to 10-X), R represents an internal resistance of the corresponding assembled battery (10-1 to 10-X), W represents an electric power of the battery pack that is higher than a predetermined electric power, SOC represents a state of charge of the corresponding assembled battery (10-1 to 10-X), t represents a time, CAP represents a full charge capacity of the cell in the corresponding assembled battery (10-1 to 10-X), M represents the number of the cells connected in parallel in the corresponding assembled battery (10-1 to 10-X), μ represents a deterioration coefficient of the cell that is a predetermined value between zero and one; wherein the current I in the expression that meets the expression is equal to or lower than a continuous allowable current (Idi_lim, Ici_lim); and the SOC in the expression falls within a range between a predetermined upper limit value and a predetermined lower limit value; and b) manufacturing each of the assembled batteries (10-1 to 10-X) by using the cells, the number of the cells being the determined number determined (M,N). a) determining a number (Mi) of the cells connected in parallel and a number (Ni) of the cells connected in series in each of the assembled batteries (10-1 to 10-X) based on the following conditions to, Ii = Voi − Vo 1 + β − β ∧ 2 − 4 αγ ∧ 0.5 × R 1 2 α Ri α = R 1 ∧ 2 × ∑ 1 Ri β = − R 1 × Vo 1 × ∑ 1 Ri − ∑ Voi Ri − Vo 1 × ∑ 1 Ri γ = W − Vo 1 × ∑ Voi Ri − Voi × ∑ 1 Ri SOCi t + Δ t = SOCi t − Ii t × Δ t 3600 × 100 CAPi × Mi × μi Ik = − ∑ Ii i = 1 ∼ k − 1, k + 1 ∼ x where: indexes 1, i and k represent the corresponding assembled battery (10-1 to 10-X), I represents a current of the corresponding assembled battery (10-1 to 10-X), Vo represents an open circuit voltage of the corresponding assembled battery (10-1 to 10-X) and depends on the number of cells connected in series in the corresponding assembled battery (10-1 to 10-X), R represents an internal resistance of the corresponding assembled battery (10-1 to 10-X), W represents an electric power of the battery pack that is higher than a predetermined electric power, SOC represents a state of charge of the corresponding assembled battery (10-1 to 10-X), t represents a time, CAP represents a full charge capacity of the cell in the corresponding assembled battery (10-1 to 10-X), M represents the number of the cells connected in parallel in the corresponding assembled battery (10-1 to 10-X), μ represents a deterioration coefficient of the cell that is a predetermined value between zero and one; wherein the current I in the expression that meets the expression is equal to or lower than a continuous allowable current (Idi_lim, Ici_lim); and the SOC in the expression falls within a range between a predetermined upper limit value and a predetermined lower limit value; and indexes 1, i and k represent the corresponding assembled battery (10-1 to 10-X), I represents a current of the corresponding assembled battery (10-1 to 10-X), Vo represents an open circuit voltage of the corresponding assembled battery (10-1 to 10-X) and depends on the number of cells connected in series in the corresponding assembled battery (10-1 to 10-X), R represents an internal resistance of the corresponding assembled battery (10-1 to 10-X), W represents an electric power of the battery pack that is higher than a predetermined electric power, SOC represents a state of charge of the corresponding assembled battery (10-1 to 10-X), t represents a time, CAP represents a full charge capacity of the cell in the corresponding assembled battery (10-1 to 10-X), M represents the number of the cells connected in parallel in the corresponding assembled battery (10-1 to 10-X), μ represents a deterioration coefficient of the cell that is a predetermined value between zero and one; wherein the current I in the expression that meets the expression is equal to or lower than a continuous allowable current (Idi_lim, Ici_lim); and the SOC in the expression falls within a range between a predetermined upper limit value and a predetermined lower limit value; and the current I in the expression that meets the expression is equal to or lower than a continuous allowable current (Idi_lim, Ici_lim); and the SOC in the expression falls within a range between a predetermined upper limit value and a predetermined lower limit value; and b) manufacturing each of the assembled batteries (10-1 to 10-X) by using the cells, the number of the cells being the determined number determined (M,N).