Battery knowledge · Capacity, energy, power and ratings
Nominal capacity
The charge a cell is rated to deliver under specified test conditions — current, temperature, rest and voltage limits — usually in ampere-hours. [1] [2]
- Also called
- rated capacity
- Unit
- Ah
Example
C-rate, current and duration
5 Ah × 1C = 5 A. Ideal duration: 1 h (60 min).
Voltage cutoff, losses, temperature and rate-dependent capacity are excluded.
Explore the graph
A C-rate becomes an actual current only when capacity is known.
5 Ah × 1C = 5 A. Ideal duration: 1 h (60 min).
I = Q × C-rate; t_ideal = 1 / C-rate
Illustrative model. Voltage cutoff, losses, temperature and rate-dependent capacity are excluded.
Use in Lemonergy
Lemonergy Core equation
Convert C-rate into current
Lemonergy Core evaluates this relation.
Equation or tool to use
- current_from_c_rate
Core equation
Inputs & settings
- Capacity (Ah)
- C-rate (1/h)
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 at 0.5C corresponds to 2.5 A. At 2C it corresponds to 10 A.
Observe. Compare the result with the equation and units.
Current magnitudes do not establish safe charge rates.
Open the worked lesson →Lemonergy Studio blocks
Capacity fit worked example
Fits charge capacity through the origin from aligned SOC-change and integrated-charge windows.
Blocks to use
- Capacity fit
Fits a positive ampere-hour capacity through the origin from aligned SOC-decrease and removed-charge windows. The weighted version accepts nonnegative window weights; zero excludes a window. A validity flag reports sufficient identifying information.
Inputs & settings
- Use the parameter values in the block reference.
- Bundled example verified on the production release of 28 October 2026.
This overview identifies the components to use. Follow the example in Lemonergy for their connections and settings.
- Review the block inputs, units and model limits.
- Open the Studio example and run its bundled model.
- Compare the output channels with the numerical checks; change one input and run again.
Example. Use the defaults below with SOC decrease per window = [0.1, 0.2, 0.3] 1 (fraction), Removed charge per window (Ah) = [0.2, 0.4, 0.6] Ah. At 0 s, Fitted capacity (Ah) is 2 Ah. Additional checks are listed below.
Observe. Inspect the outputs and numerical checks on the block reference page.
SOC and integrated charge must describe the same windows. Biased SOC or current measurements bias the fit; this operation does not collect or qualify those measurements. The example verifies numerical behavior for synthetic parameters. Cell characterization and validation for an intended use are separate tasks.
Open Studio example →Lemonergy Studio blocks
Capacity health index worked example
Endpoint-normalized health index with raw value and out-of-reference flag.
Blocks to use
- Capacity health index
Maps a measured capacity or resistance between user-selected fresh and end-of-life endpoints. It returns a clipped health index, the raw index and a flag for values outside the reference interval.
Inputs & settings
- Use the parameter values in the block reference.
- Bundled example verified on the production release of 28 October 2026.
This overview identifies the components to use. Follow the example in Lemonergy for their connections and settings.
- Review the block inputs, units and model limits.
- Open the Studio example and run its bundled model.
- Compare the output channels with the numerical checks; change one input and run again.
Example. Use the defaults below with Measured capacity (Ah) = 1.8 Ah. At 0 s, Clipped health index is 0.5 1 (fraction). Additional checks are listed below.
Observe. Inspect the outputs and numerical checks on the block reference page.
This endpoint-normalized index is not the same quantity as capacity retention. The endpoint choice determines its interpretation. The example verifies numerical behavior for synthetic parameters. Cell characterization and validation for an intended use are separate tasks.
Open Studio example →Learn it in Lesson 2 · Capacity and C-rate →
All connected Lemonergy block references
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.
- DOE Energy Storage Handbook, Chapter 16: Energy Storage Performance Testing
Sandia National Laboratories
Technical reference · Section 2.1.2.1 explains capacity, C-rate and the distinction between capacity and energy; also covers pulse characterization.
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.