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 for regulating the temperature of said cells or elements by circulation of heat-transfer fluid (FC), 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 (FC), 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 (FC), on the other hand, the or each exchange zone comprising a volume for circulation of heat-transfer fluid (FC), 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 (FC), 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 (FC), on the other hand, the or each exchange zone comprising a volume for circulation of heat-transfer fluid (FC), 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 . <EOS>