According to the invention, in an energy accumulator emulation the accuracy of energy accumulator emulation is increased in that a load current demand on the energy accumulator (20) is converted to a cell tester load current (IZ) of a real reference cell (6) based on the configuration of the energy accumulator (20) and the cell tester load current (IZ) is applied to the reference cell (6), and thereby the cell voltage (UZ) of the reference cell (6) is measured and the cell voltage (UZ) of the reference cell (6) is converted to a first energy accumulator voltage (UB) based on the configuration of the energy accumulator (20), a second energy accumulator voltage (UB_Mod) is calculated from the energy accumulator model (10) and the load current demand and the first energy accumulator voltage (UB) is compared to the second energy accumulator voltage (UB_Mod) and the energy accumulator model (10) is adjusted if the first energy accumulator voltage (UB) deviates by a specified tolerance range (TB) from the second energy accumulator voltage (UB_Mod).