Calendar aging
Also known as: SoH Degradation
Battery capacity loss that occurs over time regardless of whether the battery is cycled, reflected as a decline in State of Health (SoH). Driven by temperature and state of charge — batteries stored at high SoC and high temperatures age faster even when idle. Calendar aging combines with cycle aging to determine overall degradation, and both are accounted for in degradation curves.
In energy storage
Financial models typically account for calendar aging from the date of first cell manufacture through to the commercial operation date (COD), covering the period where batteries are produced, shipped, stored, and installed but not yet cycled. From COD onwards, cyclic degradation begins based on the contracted load profile — typically defined as one, two, or three cycles per day — and both calendar and cyclic aging are reflected in the degradation curves used to forecast augmentation schedules and warranty capacity thresholds.