BATTERY UNIT

PROBLEM TO BE SOLVED: To provide a battery unit capable of suppressing the decrease in temperature control effect.SOLUTION: A battery unit 1 comprises: a battery module group 10 consisting of a plurality of battery modules 11 that houses a plurality of electric cells, laminated one on another; a water jacket 20 placed in a direction orthogonal to a lamination direction of the battery module 11 and for heating and cooling the battery module group 10 by the coolant supplied into the inside; and a heat transfer part 30 disposed between the battery module group 10 and the water jacket 20. A projection area in a direction orthogonal to the water jacket 20, is smaller than that of the battery module group 10, and the heat transfer part 30 consists of a concave heat transfer plate 31 having a projection area being larger than that of the battery module group 10 and a heat transfer gel 32 filled into a recess part in the heat transfer plate.