Battery knowledge · Capacity, energy, power and ratings
Nominal energy
Nominal capacity times nominal voltage, in watt-hours: the headline energy figure on a datasheet. The energy actually delivered depends on the load, the temperature and how the voltage curve is weighted.
- Unit
- Wh
- Relationship
- E = Q × V_nominal
Example
Turn capacity into a nominal energy
A 5 Ah cell with a nominal voltage of 3.6 V has 18 Wh of nominal energy. This estimate uses the nominal voltage; delivered energy is the integral of measured terminal voltage multiplied by current.
Explore the graph
Voltage connects capacity in ampere-hours to nominal energy in watt-hours.
5 Ah × 12 V = 60 Wh nominal energy.
E_nominal = Q_nominal V_nominal; actual energy = ∫ VI dt
Illustrative model. Specific energy divides energy by mass; energy density divides it by volume.
Use in Lemonergy
Lemonergy Core equation
Estimate nominal energy
Lemonergy Core evaluates this relation.
Equation or tool to use
- nominal_energy_wh
Core equation
Inputs & settings
- Capacity (Ah)
- Nominal voltage (V)
This overview identifies the components to use. Follow the example in Lemonergy for their connections and settings.
- Open the lesson and inspect the equation.
- Change one input while holding the others fixed.
Example. A 5 Ah cell rated 3.6 V has 18 Wh nominal energy. Ten identical cells contain 180 Wh nominally.
Observe. Compare the result with the equation and units.
This is a rating estimate, not integrated delivered terminal energy.
Open the worked lesson →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.
- 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.
- 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.