ABSTRACT Hybrid and full electric vehicles are introducing a new era in the field of mobility. The success of this new technology depends heavily on the performance of the energy storage systems under use. As development advances further, it becomes more and more obvious that it is absolutely vital to understand and control the thermal behaviour of the energy storage system. Because design and layout of the traction battery cooling system will vary from one application to another, numerical simulation methods provide efficient tools to model, simulate and analyze the cooling system and thermal behaviour before prototypes become available for testing. In addition, simulation models can be easily subjected to arbitrary conditions and load profiles, also allowing for coupled simulations including thermal, electric and drive dynamic vehicle behaviour. This paper presents the development and layout of the thermal model of an electric vehicle traction battery. The model is created via a widely-used numerical simulation software package. In order to validate the simulation model, single-cell heat transfer simulations are carried out using computational fluid dynamics (CFD) tools. The model is intended to cover a wide range of cooling system layouts. Its modular structure allows modelling nearly any design which employs bottom plate cooling. The model is built by linking battery cells to cell packs and cell packs to cell stacks. The coolant flow through the battery system can also be exactly directed by linking the cooling channels of the various cells to each other.