The primary challenge to the commercialization of any electric vehicle is the performance management of the battery pack. The performance of the battery module is influenced by the resistance of the inter-cell connecting plates (ICCP) and the position of the battery module posts (BMP). A new battery cell model based on the Matlab–Simscape platform is developed and validated using a constant current discharge test and a pulse discharge test. Taken the ICCP as resistors, a parallel-connected battery module model (PCBMM) is established based on the battery cell model. The effect of inter-cell connecting plate resistance (ICCPR) on the battery module performance is simulated. Simulation results indicate that the ICCPR causes unevenly current flow among the battery cells. The battery cell directly connected to the BMP is the first one reaching its end-of-discharge (EOD) voltage. Also, it presents the lowest terminal voltage and state of charge (SOC) during the discharge process. The battery cell directly connected to the BMP goes into deep discharge state more easily. Therefore, it performs higher aging rate. The aging of the battery cell causes over-discharge of the adjacent battery cells. The reasonable ratio of the ICCPR to the battery ohmic internal resistance (OIR) is discussed for different average currents and different numbers of battery cells, to guarantee the maximum SOC evaluation error within a target value of 0.05.