Insertion compounds are the most promising materials for advanced rechargeable batteries. The electrochemistry of the insertion process is described here by using a novel application of the cluster variation method (CVM). This approach allows us to firmly establish the role of correlation in the analysis of the multiple plateau found in cell potential vs composition curves obtained for different host solids. The model is successfully applied to lithium cells using layered SnS2 or spinel-related LiMn2O4 solids as the active material of the positive electrode.