Aging mechanisms of graphite-LiFePO4 Li-ion batteries and accurately predicting their remaining useful life is crucial for effective battery management in energy storage systems. This study proposes a comprehensive modeling approach based on battery aging side reactions and validates its reliability through durability tests and electron microscopy characterizations. The model, which is based on single particle aging mechanisms, elucidates primary degradation reactions such as solid electrolyte interface layer growth, active material loss, and lithium plating. Durability tests under various cycling and calendar aging conditions confirm the model’s accuracy, with errors below 2%. Post-mortem analysis and material characterization tests further validate the model’s physical effectiveness using SEM, TEM, and FIB-SEM electron microscopy techniques. The findings provide valuable insights into the aging mechanisms of graphite-LiFePO4 Li-ion batteries and contribute to the development of improved battery management strategies.