Life and ageing
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%.
What it changes in practice
A cycle life figure is only comparable with another when charge rate, discharge rate, depth of discharge and temperature all match. This is the most commonly misused number in battery procurement: a claim measured at 0.5 C and 20% depth of discharge is not comparable with one measured at 1 C and 90%. Ask for the test condition before comparing quotes, and treat any figure quoted without one as marketing.
Why it matters when you specify a cell
A cycle-life number is only usable with five conditions attached: depth of discharge, charge and discharge rate, temperature, end-of-life criterion, and charge cut-off voltage. For a warranty, qualify the pack as built rather than copying the cell figure, and publish the measurement method so a dispute can be settled by measurement.
Related terms
Read further
More in Life and ageing
Other terms in this group
How cells age, and which numbers describe it honestly.
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 →Calendar life
Ageing that occurs with time rather than with use, driven mainly by temperature and state of charge during storage.
Read the entry →