A rechargeable battery is provided comprising a flexible elongate electron conductive core surrounded by a first electrochemically active layer, and a second electrochemically active layer, separated by a separation layer and where an electron conducting element contacts the outer surface of the second electrochemically active layer, whereby at least one of the two electrochemically active layers and the separation layer are comprised of thin-film layers. Further a hearing aid is provided wherein a battery comprising thin film layers is provided. Such a battery may be curled or wound to accommodate an irregular space inside the hearing aid.