This application relates a method and a control circuit for determining a charge current of a battery connected to a modulated load, wherein a current limited power source is connected in parallel to the modulated load and the battery for supplying a load dependent current up to a predetermined current limit to the modulated load and the battery. The control circuit comprises means for measuring a current flowing through the battery; means for indicating an overload condition of the current limited power source; and means for determining the charge current of the battery. The means for indicating an overload condition are configured to indicate an overload condition when a sum of a current drawn by the modulated load and a current flowing into the battery exceeds the predetermined current limit of the current limited power source.