The article presents a new method to accurately measure the state-of-charge inconsistency in lithium-ion battery packs. The researchers used a model to represent the battery's overall performance and another model to evaluate the state differences between cells. By optimizing the model's parameters and using a filtering technique, they were able to estimate the state differences effectively. An experiment with a small battery pack showed that the estimated state differences closely followed the actual values, demonstrating the method's success in tracking changes in state-of-charge.