Battery knowledge · Capacity, energy, power and ratings
Specific power
Deliverable power per unit mass, in watts per kilogram; power density is the same per litre. A cell is designed for energy or for power, rarely both: thin electrodes give power, thick ones give energy. [1]
- Also called
- power density
- Unit
- W/kg
Example
Specific power versus specific energy
The chosen example is 10 Ah at a 10-hour rating, 3.7 V constant voltage and 0.1 kg mass. At higher current, power rises while usable specific energy falls when the exponent exceeds 1.
An illustrative cell curve, not technology-region data or a fitted lithium-ion result. The empirical exponent controls the rate effect.
Explore the graph
A Ragone chart uses logarithmic axes to compare energy and power per unit mass.
The chosen example is 10 Ah at a 10-hour rating, 3.7 V constant voltage and 0.1 kg mass. At higher current, power rises while usable specific energy falls when the exponent exceeds 1.
Specific power = VI / mass; specific energy = VIt / mass
Illustrative model. An illustrative cell curve, not technology-region data or a fitted lithium-ion result. The empirical exponent controls the rate effect.
Use in Lemonergy
Separate nameplate ratings from test results.
This is a reference concept. No executable Lemonergy block has been verified for this term.
References & further reading
Technical references
- Battery Test Manual For Electric Vehicles, Revision 3
Jon P. Christopherson · Idaho National Laboratory · 2015
Technical reference · Performance characterization, pulse resistance/power, life testing and reference performance tests; historical 2015 edition.
Further reading on this topic
These sources provide broader context; they are not presented as citations for every statement in this entry.
- 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.