An apparatus can include links where each of the links includes a link-to-link mechanical interface and a link-to-link electrical interface, where the links include a circuitry link and a battery link, where the circuitry link is mechanically coupled to the battery link via at least one pair of link-to-link mechanical interfaces and where the circuitry link is electrically coupled to the battery link via at least one pair of link-to-link electrical interfaces.