Battery unit, notably for a hybrid and/or electric motor vehicle, essentially comprising, on the one hand, a plurality of cells or battery elements, if necessary physically and/or electrically grouped together in several blocks or modules, on the other hand, a housing accommodating and surrounding said cells or elements and, finally, means (4, 5) for regulating the temperature of said cells or elements by circulation of a heat-transfer fluid, comprising, at least in a bottom region on which the cells are arranged, at least one, preferentially several, heat exchange zones between said cells and the heat-transfer fluid, said zone or zones being incorporated in the structure of said housing, preferentially in the wall thereof, the or each exchange zone comprising a surface element with high thermal conductivity in contact with cells, on the one hand, and the heat-transfer fluid, on the other hand, and, the surface element with high thermal conductivity being an element added in the housing, and consisting of a metal plate, or of a similar material that is rigid and a good heat conductor, secured fluidtightly with a surface element with low thermal conductivity, each surface element with low thermal conductivity of the or each exchange zone forming an integral part of the housing and advantageously forming a portion of the wall (3', 10, 11') thereof, said battery unit being characterized in that the or each exchange zone comprises a volume for circulation of heat-transfer fluid, defined between a surface element with high thermal conductivity, in direct contact with cells, and a surface element with low thermal conductivity, in contact with the outside environment, and consisting of a portion of the bottom wall of the housing, and in that the or each circulation volume is delimited laterally or peripherally by a sealing means arranged between the two elements (7 and 9) considered, a leak path being formed around the surface element concerned, allowing the outward discharge of any heat-transfer liquid leaking if necessary from the targeted volume. comprising, at least in a bottom region on which the cells are arranged, at least one, preferentially several, heat exchange zones between said cells and the heat-transfer fluid, said zone or zones being incorporated in the structure of said housing, preferentially in the wall thereof, the or each exchange zone comprising a surface element with high thermal conductivity in contact with cells, on the one hand, and the heat-transfer fluid, on the other hand, and, the surface element with high thermal conductivity being an element added in the housing, and consisting of a metal plate, or of a similar material that is rigid and a good heat conductor, secured fluidtightly with a surface element with low thermal conductivity, each surface element with low thermal conductivity of the or each exchange zone forming an integral part of the housing and advantageously forming a portion of the wall (3', 10, 11') thereof, said battery unit being characterized in that the or each exchange zone comprises a volume for circulation of heat-transfer fluid, defined between a surface element with high thermal conductivity, in direct contact with cells, and a surface element with low thermal conductivity, in contact with the outside environment, and consisting of a portion of the bottom wall of the housing, and in that the or each circulation volume is delimited laterally or peripherally by a sealing means arranged between the two elements (7 and 9) considered, a leak path being formed around the surface element concerned, allowing the outward discharge of any heat-transfer liquid leaking if necessary from the targeted volume.