The invention is directed towards flat battery for use in a battery pack. The flat battery includes an electrode terminal that conducts to the exterior of the exterior member and connects to the battery elements within the interior region. Electrode terminals of the flat battery are formed using a connection section, and a voltage detection section that connects a voltage detection line to a control device that detects an output voltage. A notch established between the connection section and the voltage detection section mutually separates the connection section and the voltage detection section. Because of a difference in thickness between spacer sections between the connection sections and the voltage detection section, the connection section is moveable in the lamination direction of the flat battery between the spacers, while the voltage detection section is fixed.