Abstract: Electrochemical cells are mounted in a thermal control device which relies on a flow of a heat transfer fluid following round trips inside a casing thereby providing heat exchange between the heat transfer fluid and the entire wall of the electrochemical cells, and secondly, exchanges of heat which are, on average, equivalent for each electrochemical cell, regardless of its position in the thermal control device. The cells are mounted in tightly-fitting tubes arranged in the casing of the thermal control device, with their axis perpendicular to the outward and return flow directions of the heat transfer fluid inside the casing. A production process including a step of introducing the cells into the tubes is disclosed.