A battery system includes a battery that couples to an electrical system. The battery system also includes a battery control module that electrically couples to the battery. The battery control module performs a parallel current integration process on an initial state of charge using an actual capacity and a candidate capacity of the battery. Additionally, the battery control module performs a directional comparison between an estimated state of charge of the battery and results of the parallel current integration process. Further, the battery control module determines validity of the estimated state of charge based at least in part on the directional comparison between the estimated state of charge of the battery and the results of the parallel current integration process.