Electrochemical cell for use in smart cards

An electrochemical cell comprising electrodes, electrolyte and a separator, characterised in that the cell is compressible under a pressure not exceeding 100 MegaPascal to reduce reversibly the cell thickness, such that the total cell thickness is reduced by the compression by at least 5%, and that at least two external surfaces of the cell, electrically insulated from each other, are electrically conducting and are, or are in electrical contact with, respective electrodes and the cell is sealed by an impermeable, electrically non-conducting polymeric material.