Electric cars, portable electronics, and residential energy storage systems are all powered by lithium-ion batteries. Despite being better than the majority of energy storage choices, their lifespan is limited, hence performance improvement is essential for dependable use. In order to satisfy industrial and customer demands, it is imperative that these batteries function efficiently. The development of the solid electrolyte interface (SEI) layer on the anode, which also gradually raises cell resistance, is the primary cause of this slow capacity decrease. "Calendar life," on the other hand, refers to the battery's overall lifespan, which includes both storage and active use. Stressors like temperature, charge and discharge currents, and state of charge ranges can shorten battery cycle life by hastening cell deterioration. This study explores the fundamental processes that lead to lithium-ion battery degradation, looking at the effects of extended storage and frequent cycling on performance. Battery capacity is steadily reduced by degradation factors such as temperature variations and charge rates, underscoring the necessity of effective battery health management. © 2025 Elsevier B.V., All rights reserved.