Method, apparatus and system for contactless charging of an energy storage unit of an energy sink (2) by an energy source (1). Data are transferred between the energy source and the energy sink via an alternating field in a first operating mode of the energy source. In a second operating mode of the energy source, an energy necessary for charging is transferred from the energy source to the energy sink via the alternating field. In the second operating mode, no data are transferred from the energy source to the energy sink and the alternating field is therefore produced with a field strength that is greater than a possible field strength upon simultaneous transfer of data and charging energy.