Battery Electric Vehicles (BEVs) and Hybrid Electric Vehicles (HEVs) are becoming more and more relevant in the transportation sector, and it is therefore of utmost importance to find a solution to allow batteries to work safely and in a temperature range in which performance degradation or thermal runaway do not occur. To this purpose, a Battery Thermal Management System (BTMS) must be designed to ensure the correct operation of the battery pack. A BTMS can be realized in many ways; in this thesis, the BTMS that has been designed is a direct cooling system in which the battery module is immersed into the dielectric cooling liquid.