A cycle-life number belongs to a test protocol. Time spent in storage or at rest also matters, so cycle count alone does not define service years.
Cycle ageing
Charge / discharge history
Calendar ageing
Time, temperature and storage state
Two ageing histories
Cycle ageing is associated with charge/discharge use; calendar ageing concerns changes over elapsed time and storage conditions. Both histories can contribute during the same application.
Reference: INL / US DOE · Battery Test Manual for Electric Vehicles · NLR · Multi-scale modelling of battery physics
The complete cycle-life record
Check what was measured at the endpoint: retained capacity, retained energy, power capability or another agreed criterion. Also separate a stopped test from a test that reached its endpoint.
| Condition | Why it belongs with the count |
|---|---|
| Temperature | Ambient, cell temperature and test control. |
| Charge / discharge method | Rates, voltage window, rests and repetition. |
| SOC / DOD | State-of-charge window and depth of discharge. |
| Endpoint | Capacity or energy retention and other limits. |
| Mechanical condition | Fixture, constraint or pressure when specified. |
A life target is more than a division
Dividing a cycle figure by the planned annual cycle count only produces a schedule comparison. It does not include storage exposure, real load variation or a warranty commitment. For a project, provide the expected operating days, duty pattern, storage periods and required end-of-life performance.
Questions to prepare
- How many operating days and duty cycles are expected each year?
- At what temperature and SOC will the battery wait or be stored?
- What minimum capacity, energy or power must remain at the target life?
Common questions
Is 80% retention the endpoint for every product?
Use the endpoint defined by the product document and the project. Different endpoints do not support a direct cycle-count ranking.
Does little use mean no ageing?
Elapsed time and storage conditions still belong in the evaluation.