In this paper, a method for current and state of charge estimation of lithium-ion battery packs is proposed. On the basis of a fractional 1-RQ equivalent circuit cell model, a string model containing cells in serial connection, and a pack model containing strings in parallel connection is built up. In order to reduce computational costs, the model is distributed string-wise into subsystems. An algorithm using distributed fractional extended Kalman filters is applied to estimate the state of charge of all cells of each string, locally. To avoid costly measurements of numerous currents, a model based calculation is proposed which describes how the total battery current is split up between the strings. The algorithm is tested and validated using measurement data.