A thermally managed enclosure for batteries in a motor vehicle or other machinery includes a cradle of thermally conductive material for containing a battery. The cradle having a bottom wall and side walls closely fitted to and in contact with the battery, to maintain the battery in a stable position. The bottom wall of the cradle has a passageway trough containing a tube for flowing heating or cooling fluid therethrough, to control the optimal operating temperature of the battery. The passageway trough is preferably filled with a thermally conductive fill surrounding said tube. When two or more batteries are required, an array of adjacent cradles are provided in a monocoque tray formed by bonding or welding the multiple cradles at their adjacent sides. These cradles are optionally connected by linearly extending rods in the cradles