Cell voltage inconsistency of battery module is correlated with cell capacity fading inconsistency caused by uneven temperature or improper charge/discharge rate, so it is essential to study on cell voltage inconsistency when establishing a battery module capacity fade model. An accelerated life experiment is conducted on 12-series (12S) LiMn 2 O 4 battery. The evaluation index of the voltage inconsistency is given, and the evolution of the voltage of the 12S battery module is obtained. Furthermore, a model of capacity fade of this 12S battery is established based on cell voltage inconsistency, which is extended to any-series battery by means of probability distribution. Based on this extended model, the relationship between the number of cells and the life of the battery is obtained.