In this presentation, we will introduce our simulation process to design the thermal management of a full EV battery pack in two phases First Phase: The most safety-critical topic of lithium-ion batteries is thermal runaway. A thermal runaway causes a chemical reaction within the battery cell that releases considerable amounts of thermal energy and can lead to the destruction of the battery and the entire vehicle. We will introduce you to the modeling of such a process for a battery module simulated with 3D-CFD In order to determine the most appropriate cell spacing within the pack. Once the optimal cell assembly is obtained, we will then move to the second phase of this process. Second Phase: In this second phase, the most critical duty load point will be analyzed, the fast charge. 3D-CFD models offer high accuracy and enable complex geometry-dependent flow analyses in the cooling system. On the other hand, 1D system simulation offers fast computation capabilities which allows for the battery pack model integration into the vehicle model including thermal management controls. Using the example of a liquid-cooled battery for battery electric vehicle application, first, we will design the cooling system, (selecting cooling plates, etc.) and we will perform a cc-cv fast charging simulation using 3D CFD models. Second, the detailed 3D-CFD battery and cooling system model will be reduced using a machine learning approach based on neural networks to ensure the model compatibility with real-time controls. Then, the surrogate battery and cooling model will be integrated into the 1D vehicle model. The main objective of this 1D-3D cooperation is to virtually test the cooling system final design under vehicle operating conditions and using different scenarios. This workflow combines the 3D-CFD model's high accuracy with 1D fast computation capabilities which allows for driving cycle simulations while keeping accurate thermal results for the battery pack. The best of two worlds to get a robust and fast design workflow