The increasing production of lithium-ion batteries on the market highlights the importance of understanding battery degradation processes and patterns, especially calendar aging. Decreased capacity and voltage caused by long-term storage in unloaded conditions can significantly impact battery performance and lifespan. This research comprehensively evaluates the effects of storage temperature, battery chemistry (LFP and NMC), and cell form factors (prismatic, cylindrical, and pouch) on capacity retention, capacity degradation, and voltage decay rates in lithium-ion batteries stored for 60 days. Experimental quantitative testing was conducted under two storage temperatures (25°C and 37°C), accompanied by linear, geometric, and quadratic regression analyses to model the observed voltage decay patterns. The results showed that increasing the storage temperature from 25°C to 37°C notably accelerated capacity degradation and voltage decay. LFP batteries demonstrated superior capacity retention (97,79%, 97,14%, and 99,61%) and lower voltage decay rates compared to NMC batteries (96,96%). Additionally, pouch cells exhibited the highest voltage decay rates (0,77% and 0,82%) compared to cylindrical and prismatic cells. Based on statistical evaluation of the three regression models used, the quadratic regression model consistently provided the most accurate predictions for voltage decay patterns with MAPE 0,083% and R2 0,9709, making it highly recommended for precise long-term modeling of lithium-ion battery degradation.