A method for determining the state of health (SOH) of a battery is provided in which cell impedance is determined continuously, and including determining one or more confidence coefficients that depend on one or several variables selected from cell current, temperature or state of charge or their derivatives or integrals with respect to time, and continuously determining the state of health of the battery at a given point in time, using the state of health of the battery at a preceding point in time corrected as a function of cell impedance determined at the given point in time and weighted by the confidence coefficient or coefficients. The method provides a reliable way of determining the state of health of the battery with greater stability and robustness than existing methods.