NOVELTY - The device has a parallelepiped shaped flexible pouch (1) comprising a set of partitions (4, 4`, 4``, 4```) delimiting two sections (4a, 4b) of a circulation path of a heat transfer fluid. One of the sections is in contact with two chambers, and two conduits (2, 3) respectively inlets and outlets the heat transfer fluid. The pouch is made of flexible plastic material e.g. polyvinyl chloride and polyurethane.    USE - Used for being connected to a thermostatic path to control the temperature of a heat transfer fluid for controlling the temperature of a set of chambers (claimed) constituted by casings of electrochemical cells of a sealed battery e.g. lithium-ion battery, or electrochemical generator and also for controlling the temperature of a chamber in a chemical reactor, where the cells are utilized for generating large amount of energy when operating in a high-current charge or discharge mode for hybrid propulsion vehicles having a thermal combustion engine and an electric motor.    ADVANTAGE - The partitions allow for increased mechanical rigidity of the flexible pouch in comparison with a flexible pouch that does not have partitions, thus positioning the pouch in contact with the electrochemical cells of a battery in an easier manner. The partitions allow improved temperature regulation of the battery cells and permit to reduce temperature variations between the chambers. The pouch is made of flexible plastic material, thus permitting to provide the flexible pouch with reduced thickness, hence ensuring a high level of thermal exchange between the heat transfer fluid and the walls of the chambers. The chambers can have identical or different formats, identical or different material, and identical or different dimensions. The device does not generate load loss and is flexible, thus adapting the device to different configurations of the chambers.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for a method of fabricating a thermal control device for a set of chambers.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic representation of a flexible pouch.    Flexible pouch (1)    Inlet conduit (2)    Outlet conduit (3)    Partitions (4, 4`, 4``, 4```)    Sections (4a, 4b)