In a system made up of battery units (2) and corresponding terminal connectors (10), the battery units may be combined in different ways in order to obtain larger battery groups. Each battery unit (2) has one surface that forms a terminal area (3) and that includes two terminals (6, 7), this surface having longitudinal edges (4) with a length (a), and lateral edges (5) with a width (b), (a) being equal or nearly equal to (2b), and the distance of each terminal (6, 7) to the longitudinal edges (4), as well as to the adjacent narrow edge (5) being equal or nearly equal to (b/2). A terminal connector (10) connects two terminals (6, 7) of adjacent battery units (2, 2′) and includes an electrical junction (12) having two connection points (16, 17) at its ends and a span equal or nearly equal to (b). Vertical connectors may be provided to interconnect terminals of battery units belonging to different layers of stacked up batteries.