Cycle life

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Separate nameplate ratings from test results.

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Calendar life

How long a cell lasts in years, regardless of cycling, before it reaches its end-of-life criterion. It is set by calendar aging, which runs fastest at high temperature and high state of charge.

Capacity fade

The loss of charge a cell can store and deliver, for example through lithium locked into the SEI or active material that has cracked out of service.

Cycle-life test

Repeating a defined charge and discharge cycle at fixed temperature until capacity reaches the end-of-life criterion, with a reference performance test every few hundred cycles. Conditions — rate, depth of discharge, voltage window, temperature — decide the result, so they are always quoted with it.

Depth of discharge

How much of a cell’s capacity is used in a cycle. Deep cycles cause more mechanical stress in the active materials than shallow ones.

End of life

The point at which a cell no longer meets its application’s requirement, conventionally 80 % of initial capacity or a doubling of resistance. It is a definition for warranties and tests, not a point where the cell stops working.

Equivalent full cycle

Total charge throughput divided by nominal capacity, so that many shallow cycles count as the equivalent number of full ones. It lets cycle life be compared across different duty cycles.

References & further reading

Further reading on this topic

These sources provide broader context; they are not presented as citations for every statement in this entry.

1. The International System of Units (SI), 9th edition

   Bureau International des Poids et Mesures · 2026

   Topic background · Definitions of SI units and coherent derived units; 2026 revision.

2. Battery Test Manual For Electric Vehicles, Revision 3

   Jon P. Christopherson · Idaho National Laboratory · 2015

   Topic background · Performance characterization, pulse resistance/power, life testing and reference performance tests; historical 2015 edition.