The increasing demand for electric energy storage for a variety of different applications is resulting in increasing research on batteries. Designing a battery pack for a certain application requires a profound knowledge of the cells behaviour according to the requirements of a specific application. Thermal management and a good battery management system to balance and monitor the cells can greatly improve the battery lifetime and performances. This thesis focuses on the study of the cells behaviour in a battery module, which includes a battery management system (BMS) and a thermal management. For this purpose different battery modules have been designed. The major module consists of 15 lithium-Ion Polymer pouch cells, each of which has a capacity of 7 Ah. This module includes a commercial passive BMS with adaptive control and air-cooling for the thermal management. To validate the commercial passive BMS, another battery module with 15 cylindrical lithium-Ion cells was implemented. From this validation the commercial BMS was redesigned to include an air-cooling system. Beside the major module, two modules for 8 lithium-Ion Polymer pouch cells with a capacity of 8 Ah and air as thermal management were carried out. These modules serve the purpose of further experimentation on the cells behaviour. Also module designs for 15 Li-Cap cells with phase change material, air and liquid cooling for thermal management are proposed and designed with a 3D modelling program Inventor AutoCAD. To understand the behaviour of cells with a BMS two BMS’s were proposed and simulated using the Simulink/Matlab program. A simulation of a BMS with multiple resistors and a BMS with one resistor were simulated and a comparative study is given. The practical design of all battery modules are described and the experimental results are discussed in this thesis.