Battery pack modeling is essential to improve the understanding of large battery energy storage systems, whether for transportation or grid storage. It is an extremely complex task as packs could be composed of thousands of cells that are not identical and will not degrade homogeneously. This paper presents a new approach toward battery pack modeling by combining several previously published models into a comprehensive framework. This work describ. Battery pack modeling is essential to improve the understanding of large battery energy storage systems, whether for transportation or grid storage. It is an extremely complex task as packs could be composed of thousands of cells that are not identical and will not degrade homogeneously. This paper presents a new approach toward battery pack modeling by combining several previously published models into a comprehensive framework. This work describes how the sub-models are connected, their basic principles, what adjustments were necessary, and what new parameters needed to be introduced. Overall, this paper introduces an open modular framework for future work on, among others, the impact of cell-to-cell variations, inhomogeneous degradation, SOC and SOH tracking, balancing and performance forecast.••••New modular battery pack modeling approach.••The model considers cell-to-cell variations at the initial stage and upon aging.••New parameter for imbalance prediction: degradation ratio charge vs. discharge.Li-ion batteriesCell-to-cell variationsInhomogeneitiesPack modelingSeriesParallelIn recent years, there has been a great momentum of aggressive goals towards cleaner energy portfolios from stakeholders, local or federal. Per example, the state of Hawai´i have goals of 100% clean energy and transportation by 2045 [1,2]. With the projected high penetration of electric vehicles and electrochemical energy storage, there is a need to understand and predict better the performance and durability of large battery packs. Recent studies reiterated that batteries are susceptible to usage and that small differences in duty cycle could have a significant impact on the durability. This precludes the use of black-box battery degradation models and highlights the need for a new battery pack model that can take all these aspects into consideration. This will prove especially valuable to assess the real impact/cost relationship of battery energy storage systems (BESS), new [4,5] or recycled, directly on the grid as well as in electric vehicles for driving or as grid support.Battery pack modeling is intricate because of the number of parameters to consider. On top of an excellent single cell (SC) model, a battery pack model also needs to consider SCs small manufacturing and aging differences [,,,,,,,,, ]. These slight variations could drastically influence the overall assembly performance and durability [,,, ] and, as a result, all SCs should be considered independently while modeling t. Fig. 2 presents the model algorithm. The simulation starts with the first step of the requested duty cycle at a time t = 0. The model first calculates the full electrochemical response of all SCs independently based on their characteristics and their SOH (SC engine). This will be repeated at every SOH. Each of the SC ECMs can be parameterized eithe.
