Abstract: A state of battery testing system is disclosed which includes a charger, a load to be coupled across the battery's positive and negative terminals, a processer adapted to apply a predetermined voltage pulse across the battery's positive and negative terminals, apply the load to the battery, measure and log current through the load as Iexp, and establish a model based on establishing an initial estimation of state of the battery (?0), and establishing a modeled state of battery (?i) based on a plurality of internal parameters of the battery. The model is adapted to output a model current through the load, inputting ?0 and the plurality of internal parameters of the model to thereby generate Imodel, generate an objective function (f) based on a comparison of Imodel and Iexp, and iteratively optimize ?i, and output ?optimal based on the iterations.