Battery unit, notably for a hybrid and/or electric motor vehicle, essentially comprising, on the one hand, a plurality of battery cells or elements, if necessary grouped together physically and/or electrically 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 heat-transfer fluid, the housing comprising, at least in a bottom region on which the cells are arranged, at least one zone for exchanging heat between said cells and the heat-transfer fluid, said zone or zones being incorporated in the structure of said housing, 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, the or each exchange zone comprising 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, said battery unit being characterized in that the housing is made of a rigid material with low thermal conductivity and consists, on the one hand, of a bottom tray, with a bottom wall and lateral walls (10"), and of a top cover, in that the bottom region comprises several heat exchange zones each comprising a surface element with high thermal conductivity, each of which is an element added in the housing and consists of a metal plate or of a similar material that is rigid and a good heat conductor, liquid-tightly secured to a surface element with low thermal conductivity, and in that each surface element with high thermal conductivity in the form of a plate is secured to the wall of the housing, on the one hand, peripherally, by mechanical attachment or welding, and, on the other hand, in a plurality of bonding zones situated inside the surface of said plate and distributed over the surface of said plate, preferentially regularly, each of the plates being associated with the cells of a module. the housing comprising, at least in a bottom region on which the cells are arranged, at least one zone for exchanging heat between said cells and the heat-transfer fluid, said zone or zones being incorporated in the structure of said housing, 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, the or each exchange zone comprising 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, said battery unit being characterized in that the housing is made of a rigid material with low thermal conductivity and consists, on the one hand, of a bottom tray, with a bottom wall and lateral walls (10"), and of a top cover, in that the bottom region comprises several heat exchange zones each comprising a surface element with high thermal conductivity, each of which is an element added in the housing and consists of a metal plate or of a similar material that is rigid and a good heat conductor, liquid-tightly secured to a surface element with low thermal conductivity, and in that each surface element with high thermal conductivity in the form of a plate is secured to the wall of the housing, on the one hand, peripherally, by mechanical attachment or welding, and, on the other hand, in a plurality of bonding zones situated inside the surface of said plate and distributed over the surface of said plate, preferentially regularly, each of the plates being associated with the cells of a module.