an electrical apparatus includes a body for consuming power ; a battery for supplying power to the body , wherein the body is capable of detecting an installation of the battery into the body , correlating the installation of the battery to a current real - time date , and displaying the date on which the battery was first installed in the body ; and a display of a full charge capacity of the battery , the full charge capacity being calculated by comparing an actual present capacity of the battery to an estimated present capacity of the battery .