After the aging of the single battery is completed, it enters the stage of module combination. Before the combination, it is necessary to first screen, that is, test the capacity, dynamic internal resistance and voltage of the single battery, and try to select batteries with the parameters for matching.

A larger battery pack usually consists of multiple battery modules. Each battery module is composed of multiple single cells in series and parallel. The series connection can increase the voltage of the battery module, and the parallel connection can increase the capacity of the battery module. The principle followed when matching single cells for battery modules is generally to give priority to capacity in series, so as to reduce the overcharge or overdischarge of modules with lower capacity during the charging and discharging process of the battery pack. In parallel connection, internal resistance is given priority to avoid overcharging or overdischarging batteries with small internal resistance caused by uneven current distribution during high current charging and discharging.

After completing the matching of the single cells, it enters the assembly process of the battery module. This process usually fixes the matched single cells into the module structure of the battery pack, and then uses the bus bar to connect the single cells. The electrode poles are connected together.