The engineering decision
Select the method from the decision being made and compare values only when excitation, time or frequency and operating conditions match.
Have these inputs ready
- Required load or screening decision
- Instrument excitation and reported quantity
- Frequency or pulse sampling time
- Cell SOC, temperature and history
Alternative methods for different measurement questions
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Separate the measurement definitions
DCIR uses a defined current step and a voltage difference at stated times. AC resistance or impedance uses a small alternating signal at a stated frequency. EIS measures complex impedance across a frequency range. For the DC pulse calculation, define discharge current as positive and use Rapp(t) = [Vbefore − V(t)] / [I(t) − Ibefore], with matched voltage and current sampling times.
ESR is ambiguous in battery work unless the instrument, circuit mode and derivation are stated. Replace the shorthand with the actual measurement definition.
| Method | Result | Suitable starting use |
|---|---|---|
| DC pulse | Rapp(t) with the defined baseline and current sign | Representative load sag |
| AC point | Frequency-specific impedance result | Controlled production screening |
| EIS | Complex spectrum versus frequency | Characterization and model fitting |
| ESR label | Instrument-dependent simplified value | Use only with its explicit definition |
Do not substitute one method without correlation
A 1 kHz value is not a substitute for a multi-second pulse result. However, the timescale study found agreement across techniques at matched observation timescales. Comparable conditions and correlation are required; there is no universal AC-to-DC conversion factor.
A fast screening method can still be valuable when the fixture and conditions are controlled and its acceptance limit has been correlated with the required performance.
References: A study of the influence of measurement timescale on internal resistance characterisation methodologies for lithium-ion cells; Comparison of Several Methods for Determining the Internal Resistance of Lithium Ion Cells
Put the definition beside the number
Record excitation amplitude, frequency or pulse time, reported impedance component, SOC, temperature, rest, fixture and calculation.
Milliohms alone are not a comparable specification.
Measurement & validation procedure
| Test / review | Record | Acceptance condition |
|---|---|---|
| Identify the reported quantity | Instrument mode, excitation and calculation | DC resistance, impedance magnitude and real component are not conflated |
| Control comparison conditions | SOC, temperature, rest and fixture | Compared values use matched conditions |
| Validate the acceptance limit | Screening result versus required performance | Correlation and allowed error are documented |
Continue this engineering task
Related engineering guidance
Prepare the evidence for review
- Instrument method and configuration
- Raw pulse or impedance data
- Controlled SOC and temperature record
- Correlation to the application acceptance test
Technical sources & claim support
References support the stated engineering principles. Worked examples use their explicitly stated assumptions.
- Comparison of Several Methods for Determining the Internal Resistance of Lithium Ion Cells ↗
Sections 4–5: DC step, AC resistance, impedance spectroscopy and pulse-duration effects
Peer-reviewed method comparison. The proposed timing and cell values are not universal acceptance requirements.
- A study of the influence of measurement timescale on internal resistance characterisation methodologies for lithium-ion cells ↗
Scientific Reports 8, 21 (2018); abstract and Figure 7: comparison at matched measurement timescales
Peer-reviewed cell study. Numerical values apply only to the tested cells, SOC, temperature and equipment.
- Nonlinear Electrochemical Impedance Spectroscopy for Lithium-Ion Battery Model Parameterization ↗
Structural parameter identifiability and conclusions: nonlinear single-particle model
Peer-reviewed primary research. Single-particle physical model; extending the identifiability lesson to other model families is an engineering inference.
Key claims and evidence
| Claim | Basis | Reference |
|---|---|---|
| DC, AC and impedance-spectroscopy methods produce method-dependent results | documentation | Comparison of Several Methods for Determining the Internal Resistance of Lithium Ion Cells |
| Using fitted impedance parameters requires checking model identifiability and application correlation | workflow | engineering workflow |
| ESR should be replaced by the explicit instrument definition in battery specifications | workflow | engineering workflow |