Life and ageing
Calendar life
Ageing that occurs with time rather than with use, driven mainly by temperature and state of charge during storage.
What it changes in practice
A cell that is never cycled still ages. Storage at high temperature and high state of charge accelerates it; cool storage at moderate SoC slows it. For stationary storage and backup applications, where the pack may sit near full charge for most of its life, calendar ageing can dominate over cycle ageing. This is why storage warranty terms specify both a cycle count and a calendar period.
Why it matters when you specify a cell
Cells age while idle, dominated by storage temperature and state of charge. A product that cycles twice a week will meet its warranty date long before its cycle count, so calendar behaviour — not cycle life — is the number that matters. Store at partial charge, keep it cool, and write both conditions into the warranty.
Related terms
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More in Life and ageing
Other terms in this group
How cells age, and which numbers describe it honestly.
Cycle life
The number of charge and discharge cycles a cell completes before its capacity falls below a stated fraction of its original value, usually 80%.
Read the entry →Depth of discharge (DoD)
The fraction of a cell capacity removed during a discharge, expressed as a percentage.
Read the entry →State of charge (SoC)
The remaining charge in a cell at a given moment, expressed as a percentage of its current usable capacity.
Read the entry →State of health (SoH)
The current condition of a cell expressed as a percentage of its original capability, usually capacity, sometimes resistance.
Read the entry →