A method and apparatus for simulating the operation of a rechargeable battery. A value is obtained for at least one parameter that describes an internal state of the battery. The obtained value is used for calculating a prediction value for a characteristic of the battery that is observable outside the battery. These steps are repeated a multitude of times in order to simulate the operation of the battery over a certain period of time. A difference is detected between a calculated prediction value and a known value of a corresponding characteristic in a corresponding situation. The obtained value of the at least one parameter is corrected before a further prediction value is calculated by an amount that is proportional to the detected difference.