Patent ID: 7723956

Claim:
A battery module system comprising: a battery module comprising battery units which are connected in series, each of the battery units comprising a unit cell having a voltage variation rate A mV/% SOC at a full charge voltage V H1 (V) larger than 20 mV/% SOC, which is a value obtained when the unit cell is charged at a current of 1 C at 25° C. a current supply member which supplies current to the battery module; a voltage detecting member which detects a voltage of the unit cells; and a control member which controls the current to a current I 1 until at least one unit cell reaches the full charge voltage V H1 (V) and then controls a voltage of the battery module to a voltage V 2 (V) given by the following equation (1): V 2 =V H2 ×n (1) where V H2 is a voltage lower than a voltage V MI of the unit cell, where V M1 is a rate of variation point where rate of variation is 20 mV/% SOC, when the voltage variation rate A mV/% SOC reaches 20 mV/% SOC from less than 20 mV/% SOC and n denotes the number of battery units connected in series.