The present invention relates toa method for determination of the state-of- charge (SoC) of a rechargeable battery as a function of the Electro-Motive Force (EMF) prevailing in said battery. The invention also relates to a method for measuring the relation between the state-of-charge (SoC) and the EMF. The invention further relates to an apparatus for determination of the State-of-Charge (SoC) of a rechargeable battery as a function of the Electro-Motive Force (EMF) prevailing in said battery