A charger apparatus for charging and discharging a battery module series, the battery module series comprising at least three battery modules (10_1, 10_2, 10_3, 10_4, 10_i, 10_j, 10_k or 10_n) mutually connected in series, a j-th battery module (10_j) of the battery modules connected between a i-th battery module (10_i) and a k-th battery module (10_k) of the battery modules, the charger apparatus comprising a plurality of chargers (100_1, 100_2, 100_3, 100_4, 100_5, 100_a, 100_b, 100_c, 100_d or 100_m), the chargers (100_1, 100_2, 100_3, 100_4, 100_5, 100_a, 100_b, 100_c, 100_d or 100_m) being at least grouped into a first charger group and a second charger group, and the chargers (100_1, 100_2, 100_3, 100_4, 100_5, 100_a, 100_b, 100_c, 100_d or 100_m) comprising: a first charger (100_1, 100_2, 100_5, 100_a or 100_b) grouped into the first charger group, wherein a charging current output terminal of the first charger (100_1, 100_2, 100_5, 100_a or 100_b) is coupled to a positive terminal of the i-th battery module (10_i), and a charging current input terminal of the first charger (100_1, 100_2, 100_5, 100_a or 100_b) is coupled to a first node which is between the j-th battery module (10_j) and the k-th battery module (10_k); and a second charger (100_3, 100_4, 100_5, 100_c, 100_d or 100_m) grouped into the second charger group, wherein a charging current output terminal of the second charger (100_3, 100_4, 100_5, 100_c, 100_d or 100_m) is coupled to a second node which is between the i-th battery module (10_i) and the j-th battery module (10_j), and a charging current input terminal of the second charger (100_3, 100_4, 100_5, 100_c, 100_d or 100_m) is coupled to a negative terminal of the k-th battery module (10_k), the charger apparatus being characterized in that if a configuration matrix A represents a charging relationship between the chargers (100_1, 100_2, 100_3, 100_4, 100_5, 100_a, 100_b, 100_c, 100_d or 100_m) and the battery modules (10_1, 10_2, 10_3, 10_4, 10_i, 10_j, 10_k or 10_n), the configuration matrix A is not an identity matrix, wherein charging and discharging operation conducted by each one of the chargers (100_1, 100_2, 100_3, 100_4, 100_5, 100_a, 100_b, 100_c, 100_d or 100_m) is independent of charging and discharging operation conducted by another one of the chargers. a first charger (100_1, 100_2, 100_5, 100_a or 100_b) grouped into the first charger group, wherein a charging current output terminal of the first charger (100_1, 100_2, 100_5, 100_a or 100_b) is coupled to a positive terminal of the i-th battery module (10_i), and a charging current input terminal of the first charger (100_1, 100_2, 100_5, 100_a or 100_b) is coupled to a first node which is between the j-th battery module (10_j) and the k-th battery module (10_k); and a second charger (100_3, 100_4, 100_5, 100_c, 100_d or 100_m) grouped into the second charger group, wherein a charging current output terminal of the second charger (100_3, 100_4, 100_5, 100_c, 100_d or 100_m) is coupled to a second node which is between the i-th battery module (10_i) and the j-th battery module (10_j), and a charging current input terminal of the second charger (100_3, 100_4, 100_5, 100_c, 100_d or 100_m) is coupled to a negative terminal of the k-th battery module (10_k), the charger apparatus being characterized in that if a configuration matrix A represents a charging relationship between the chargers (100_1, 100_2, 100_3, 100_4, 100_5, 100_a, 100_b, 100_c, 100_d or 100_m) and the battery modules (10_1, 10_2, 10_3, 10_4, 10_i, 10_j, 10_k or 10_n), the configuration matrix A is not an identity matrix, wherein charging and discharging operation conducted by each one of the chargers (100_1, 100_2, 100_3, 100_4, 100_5, 100_a, 100_b, 100_c, 100_d or 100_m) is independent of charging and discharging operation conducted by another one of the chargers.