The nominal value is defined under specific test conditions — typically 25°C and a C/5 or C/2 discharge rate per IEC 61960-3 — and should not be treated as the capacity available under all operating conditions. At higher discharge rates or lower temperatures the delivered capacity will be lower; at very low rates and elevated temperatures it may slightly exceed the nominal figure. This is why the test conditions must always accompany any quoted capacity value.
Nominal vs rated capacity
Some manufacturers publish a rated capacity that is slightly lower than the measured nominal capacity, providing a built-in tolerance margin. Under IEC 61960-3, the measured discharge capacity must meet or exceed the declared rated value. In incoming quality control, a tighter acceptance band — typically ±2% of nominal — is commonly applied to screen for capacity spread within a production batch.
Nominal capacity as the SoH baseline
Nominal capacity measured on a new cell provides the reference value for state of health (SoH) calculations throughout the cell’s service life. As the cell ages, periodic capacity measurements under the same standard conditions track the decline. End of life in automotive applications is conventionally defined at 80% of the original nominal capacity.
For the full test procedure used to establish nominal capacity, see Cell Capacity Test Procedure.
See also: Nominal Energy, Nominal Voltage