A rechargeable set of electrochemical cells, or a single cell, designed to store chemical energy and release it in the form of electrical energy to provide power for active implantable medical devices or external medical instruments, for backup power for programmable devices that must retain electronic information, or to power portable or other medical devices when it is not possible or convenient to use the line supply. The size, shape, and chemical composition of the battery should be specified according to the requirements of the appropriate IEC standard.