Modular series-connected battery pack (BIMoSe) consisting of lithium battery cells (10, 11, 12, 13, 14, 15, 16, 17) arranged in a vertical direction; these cells (10, 11, 12, 13, 14, 15, 16, 17) with the same characteristics are connected in series by connections in a given direction corresponding to the direction of the currents to obtain the necessary voltage, characterized in that the modular series-connected battery pack comprises, in the same direction, a pair of upper and lower holding elements for holding adjacent cells (10, 11, 12, 13, 14, 15, 16, 17) and perpendicular to the direction S; wide tongues (30 n) connecting, on each upper or lower face of the module, each pair of adjacent cells (10, 11, 12, 13, 14, 15, 16, 17) mounted in series each with the next by their poles of opposite polarity, in the direction S, ensure the connections between the battery cells (10, 11, 12, 13, 14, 15, 16, 17), said wide tongues of each upper, respectively lower, face being offset by one cell on the other lower, respectively upper, face; the connections being also connected to a processing circuit for measuring the potentials of each cell, the circuit being mounted on a printed circuit assembly forming three surfaces arranged in a U, said U-shaped assembly enveloping the modular battery assembly on three sides, said U-shaped assembly being arranged so that the normal to the central part of the U is perpendicular to the direction S and to the vertical direction V, and the outer face of the central part of the U comprises the electronics of the management system of the modular battery pack (BIMoSe); at least one Battery Management System, forming the central part of the U, arranged vertically, comprises the heating resistors of the modular battery pack and these resistors are connected on command from the management circuit to one or more battery cells (10, 11, 12, 13, 14, 15, 16, 17) of the modular battery pack for their supply; the lower part of the U arranged under the cells (10, 11, 12, 13, 14, 15, 16, 17) contributes, with the upper part of the U, at least to recovering the potentials of each of the cells (10, 11, 12, 13, 14, 15, 16, 17) of the modular battery pack in order to supply them to the voltage management circuit of the modular battery pack management system. wide tongues (30 n) connecting, on each upper or lower face of the module, each pair of adjacent cells (10, 11, 12, 13, 14, 15, 16, 17) mounted in series each with the next by their poles of opposite polarity, in the direction S, ensure the connections between the battery cells (10, 11, 12, 13, 14, 15, 16, 17), said wide tongues of each upper, respectively lower, face being offset by one cell on the other lower, respectively upper, face; the connections being also connected to a processing circuit for measuring the potentials of each cell, the circuit being mounted on a printed circuit assembly forming three surfaces arranged in a U, said U-shaped assembly enveloping the modular battery assembly on three sides, said U-shaped assembly being arranged so that the normal to the central part of the U is perpendicular to the direction S and to the vertical direction V, and the outer face of the central part of the U comprises the electronics of the management system of the modular battery pack (BIMoSe); at least one Battery Management System, forming the central part of the U, arranged vertically, comprises the heating resistors of the modular battery pack and these resistors are connected on command from the management circuit to one or more battery cells (10, 11, 12, 13, 14, 15, 16, 17) of the modular battery pack for their supply; the lower part of the U arranged under the cells (10, 11, 12, 13, 14, 15, 16, 17) contributes, with the upper part of the U, at least to recovering the potentials of each of the cells (10, 11, 12, 13, 14, 15, 16, 17) of the modular battery pack in order to supply them to the voltage management circuit of the modular battery pack management system.