A charging surface comprising multiple conductive regions can be used to charge an electronic device placed on it the surface so that electrodes on the device engage respective conductive regions of the surface. In order to distinguish such chargeable devices from short circuits and other spurious connections, the coupling interface associated with the charging surface is controlled so as to establish a text voltage across each pair of conductive regions in sequence, and look for pairs of conductive region demonstrating a voltage drop characteristic of a particular class of device. Relationships between every pair of conductive regions can be determined and recording, and the voltage level supplied to each conductive region set accordingly. The coupling interface may furthermore operate to identify device classes, and to set supply voltages or establish additional connections on the basis of stored device class information. Discrimination on the basis of voltage drop can be enhanced by the provision of a coupling adapted associated with a device to be detected, where the coupling adapter demonstrates an anti-inversion characteristic, for example implemented with a MOSFET, across at least a pair of these electrodes.