This presentation shows a complete model for an li-ion battery pack. It starts from the Newman electrochemistry model to create the battery performance curves. Such information is then used to create cell level battery equivalent circuit model (ECM). 28 cell ECMs are connected to create the module ECM. Four module ECMs are connected through a busbar model to create the pack ECM. The busbar model is a reduced order model (ROM) extracted from electromagnetics FEA solver, taking into account the parasitic effects. Battery thermal performance is first calculated by computational fluid dynamics (CFD). Then, a thermal ROM is created out of CFD solution. The thermal ROM is then two-way coupled with the battery pack ECM to form a complete battery pack model. Thanks to the ROM technology, such a battery pack model can finish a complete charge discharge cycle within seconds of simulation time.