A real battery ages in two ways at once, and understanding both helps you estimate how long a pack will actually last.

How Do Calendar Life and Cycle Life Relate?

Two Ways a Battery Ages

Cycle life counts charge-discharge cycles and reflects wear from repeated use. Calendar life is how long a cell lasts simply by existing, regardless of use, driven by time-related chemical decay. A battery suffers both mechanisms simultaneously.

What Drives Each

Cycle aging is accelerated by deep discharges, high charge rates and high temperatures. Calendar aging is driven mainly by high temperature and high state of charge: a cell stored fully charged in a hot room ages faster even if it is never used. Side reactions and self-discharge continue whenever the cell exists.

Together they determine end of life. To maximise both, avoid storing at 100% charge in heat, use moderate charge rates, keep depth of discharge shallow where possible and cool the pack. For long-life products, define the required service years and duty cycle so the right chemistry and BMS strategy are chosen during project evaluation.