Abstract: Lithium-ion battery is one of the candidates for energy storage for hybrid aircraft. The study herein is intended to investigate the performance and longevity of hybrid aircraft Li-ion battery packs. A physical empirical model along with testing were presented to address the behavior of Li-ion batteries during discharge cycles and storage. The model includes three sub-models to study all effects around the batteries, electrical, thermal, and wear models. This study was linked to the cabin, thermal effects, and environmental conditions. Results were integrated with different equations to obtain required variables. Then, these results were validated using testing of cells under needed conditions to have results compared to aircraft packs. The testing is conducted the cell life during cycling and storage under time, number of cycles and associated with other factors such as temperature, voltage, capacity and C-rate. To overcome the long period of testing during storage, accelerated testing method at different temperatures was used. At the end of cells life with remaining capacity due to degradation after certain time, these cells can be used in another application.