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Before a battery can be qualified for flight, engineers must first understand how it behaves.
Battery characterisation testing is the controlled measurement of the electrical, thermal and performance characteristics of a cell, module or battery assembly. It establishes the baseline needed for credible design, qualification, acceptance and life-testing programmes.
Within a space programme, characterisation is not simply a laboratory exercise. The resulting data can support power-system sizing, operating-limit definition, battery modelling, mission-life analysis, environmental-test planning and assessment of performance changes after storage, cycling or environmental exposure. Without controlled baseline data, subsequent testing can produce results that are difficult to interpret or compare.
ECSS-E-HB-20-02A identifies relevant characterisation activities including capacity and energy measurement, internal resistance, AC impedance, self-discharge, charge retention, rate capability and cell electromotive-force measurement. These measurements are condition-dependent. Temperature, state of charge, charge method, discharge rate, voltage limits, rest periods and test history must therefore be controlled and recorded.
For New Space organisations, early characterisation can expose capacity variation, resistance differences, thermal sensitivity and manufacturing variability before expensive qualification hardware is committed.
For programme managers, characterisation reduces uncertainty. For engineers, it provides evidence for informed design decisions. For spacecraft programmes, it replaces optimistic assumptions with measurable data.
Battery characterisation testing is the structured measurement of a battery’s electrical, thermal and performance parameters under controlled conditions to establish its behaviour, capability and limitations.
The test article can be:
An individual cell.
A series or parallel string.
A cell building block.
A module.
A complete battery.
Evidence obtained at one test-item level is not automatically representative of another. Cell-level results should not be treated as complete proof of integrated battery behaviour without technical justification.
Characterisation seeks to answer fundamental engineering questions:
What usable capacity is available under defined conditions?
How much energy can be delivered over the specified voltage range?
How does performance change with temperature?
How does internal resistance vary with state of charge and test history?
How does impedance vary with frequency?
How quickly does the test article self-discharge?
How well does it retain charge?
How does it respond to different charge and discharge rates?
What changes occur after environmental exposure or cycling?
Are the assumptions used in battery models supported by test data?
Characterisation does not independently prove mission life or qualify a complete battery. It provides inputs and baseline evidence for those wider activities.
Characterisation supports:
Cell selection.
Battery architecture.
Electrical operating limits.
Thermal design.
Power-system sizing.
Energy-margin assessment.
Battery-model development.
Testing can identify:
Cell-to-cell variation.
Lot-to-lot variation.
Material or process changes.
Differences between supplier data and measured performance.
Early signs of manufacturing inconsistency.
Baseline and health checks can be used before and after AIT to assess whether battery condition has changed.
The flight battery should not be used unnecessarily during AIT. Storage history, state of charge and open-circuit voltage should remain controlled.
Characterisation data can support:
Qualification.
Acceptance.
Life testing.
Verification matrices.
Verification Control Document closure.
Engineering analysis.
Test-result interpretation.
Characterisation evidence contributes to customer or design-authority assessment of battery condition and expected performance.
The test facility does not independently approve the battery for flight.
Many battery problems originate from incorrect assumptions rather than an obvious hardware defect.
Characterisation can identify:
Cell-to-cell variation.
Capacity below expectation.
Energy limitations.
Thermal sensitivity.
Resistance growth.
Impedance changes.
Unexpected self-discharge.
Poor charge retention.
Rate-capability limitations.
Voltage divergence.
Changes following storage or environmental testing.
Identifying these issues early can prevent unsuitable hardware, operating limits or models from progressing into qualification.
ECSS-E-HB-20-02A discusses capacity and energy measurement, internal resistance, AC impedance, self-discharge, charge retention, rate capability and cell electromotive-force measurement as relevant battery test activities.
The handbook provides guidance rather than one universal mandatory programme.
The controlling obligations are established through:
The project requirement baseline.
The business agreement.
Invoked ECSS standards.
Customer specifications.
Approved tailoring.
The verification plan.
The test specification.
Characterisation generates measurable evidence supporting:
Battery models.
Verification matrices.
Qualification planning.
Mission analyses.
Power budgets.
Life-test interpretation.
Performance-retention assessment.
Comparison before and after environmental testing.
Confidence depends upon consistent conditions. Results from different temperatures, charge methods or discharge rates should not be compared as though they were equivalent.
A battery can survive vibration or thermal-vacuum testing and still be unsuitable for its mission if the underlying performance assumptions are wrong.
Characterisation helps determine whether the battery can provide the required charge, energy and power under relevant conditions.
It also creates a reference against which later degradation can be measured.
Documents that can be relevant include:
ECSS-E-HB-20-02A: Guidance on lithium-ion battery testing and documentation.
ECSS-E-ST-20: Electrical and electronic engineering requirements.
ECSS-E-ST-10-02: Verification planning, control and evidence.
ECSS-E-ST-10-03: Test planning, specifications, procedures and execution.
ECSS-E-ST-10-04: Space-environment definition where environmental conditions affect the test.
ECSS-Q-ST-20: Quality-assurance requirements where invoked.
ECSS-Q-ST-20-08: Storage, handling and transportation of space hardware.
ECSS-S-ST-00: Application of the ECSS system and customer-supplier requirements.
Only documents genuinely applicable to the project should form part of the controlled baseline.
ECSS-E-HB-20-02A is a supporting handbook. It provides guidance, recognised test approaches, recommendations and good practice.
It does not:
Establish one universal characterisation programme.
Define universal pass criteria.
Replace the project test specification.
Automatically make every described test mandatory.
Qualify a battery by itself.
Characterisation should consider:
Mission duration.
Orbit type.
Eclipse profile.
Power-demand profile.
Cell chemistry.
Cell construction.
Battery architecture.
State-of-charge range.
Charge and discharge rates.
Operating temperature range.
Voltage limits.
Model philosophy.
Available heritage.
Supplier data.
Sample quantity.
Manufacturing-lot variation.
Customer verification philosophy.
Prime contractors, agencies and programme customers can specify:
Characterisation temperatures.
State-of-charge conditions.
Charge protocols.
Discharge rates.
End-of-charge voltages.
End-of-discharge voltages.
Rest periods.
Pulse-current conditions.
Frequency ranges.
Sample quantities.
Measurement accuracy.
Data-acquisition rates.
Reporting requirements.
Acceptance or alert limits.
These requirements should be recorded in the approved test specification, not assumed from a handbook example.
Establish the engineering and verification objectives.
Identify the applicable requirements.
Define the test article and configuration.
Select representative sample quantities.
Record cell lot and manufacturing information.
Define the parameters to be measured.
Establish temperature and state-of-charge conditions.
Define charge and discharge methods.
Establish measurement accuracy and uncertainty requirements.
Define success, alert and failure criteria.
Establish how the results will be used.
Approve the test plan and procedure.
Inspect and identify the test articles.
Record activation and storage history.
Confirm state of charge.
Configure electrical connections.
Configure thermal control.
Confirm sensor positions.
Verify instrumentation ranges.
Confirm calibration status.
Establish data-acquisition settings.
Review stored-energy and battery hazards.
Complete the test readiness review.
Stabilise the test article at the required temperature.
Perform the approved conditioning sequence.
Apply the defined charge protocol.
Observe required rest periods.
Apply the defined discharge or pulse profile.
Record voltage, current, temperature and time.
Calculate the approved performance parameters.
Repeat measurements where required.
Record interruptions, deviations and anomalies.
Retain the raw data.
Compare results with supplier data and design assumptions.
Review repeatability.
Assess cell-to-cell and lot-to-lot variation.
Examine temperature dependence.
Assess state-of-charge dependence.
Evaluate changes from previous baselines.
Review anomalies and nonconformances.
Confirm whether the results remain representative.
Determine whether additional testing is required.
Issue the controlled test report.
Record the test-item configuration.
Document all test conditions.
Provide raw and processed data.
State the calculation methods.
Record measurement uncertainty where required.
Document deviations and nonconformances.
Establish the approved baseline dataset.
Update models, verification evidence and outstanding actions.
Capacity is the charge available from a cell or battery under defined conditions and is normally expressed in ampere-hours.
A capacity measurement can include:
Discharge to the defined end-of-discharge condition.
Recharge using the approved method.
Required rest or taper conditions.
Discharge at a specified current or power.
Termination at the approved cut-off voltage.
Calculation of delivered capacity.
The result depends on:
Temperature.
Charge method.
Charge current.
End-of-charge voltage.
Taper condition.
Rest period.
Discharge current or power.
End-of-discharge voltage.
Test-item age and history.
Capacity values should not be reported without their measurement conditions.
Energy measurement determines the electrical energy delivered during discharge and is normally expressed in watt-hours.
Energy is affected by both the current and the changing terminal voltage.
It is particularly relevant where the mission requirement concerns usable energy rather than charge alone.
The report should identify:
Start and end voltage conditions.
Temperature.
Discharge current or power.
Charge protocol.
Integration method.
Sampling rate.
Any excluded or invalid data.
Internal resistance characterises opposition to current flow within the cell or battery.
It can be estimated using:
Current pulses during discharge.
Controlled changes in current.
Current interruption.
Measured voltage response.
Using Ohm’s law, resistance can be calculated from the change in voltage divided by the change in current.
The measurement conditions should include:
State of charge.
Temperature.
Charge or discharge direction.
Baseline current.
Pulse current.
Pulse duration.
Measurement time.
Sampling rate.
Internal-resistance data can support power analysis, voltage-drop assessment, thermal modelling and ageing evaluation. It does not, by itself, explain the precise physical cause of a change.
AC impedance measurement characterises the test item over a defined frequency range at a specified state of charge and temperature.
The result can support:
Comparison between cells.
Baseline characterisation.
Assessment of change after cycling.
Assessment of change after storage.
Model development.
Investigation of frequency-dependent behaviour.
Interpretation should be technically controlled. Changes in impedance can have multiple causes. A specific ageing mechanism should not be claimed without an appropriate model and supporting evidence.
Self-discharge is reversible capacity loss while no current is supplied to an external circuit.
A self-discharge test can include:
A standard capacity measurement.
Adjustment to a defined state of charge.
Storage at a controlled temperature.
Open-circuit-voltage monitoring.
Discharge after the specified rest period.
A repeated capacity measurement.
The results can distinguish the effects of self-discharge from irreversible performance loss, provided the test method and analysis are suitable.
Charge retention assesses how much charge remains after a defined period at a specified temperature and state of charge.
The activity can involve:
Charging or discharging to a defined state of charge.
Holding the test article in open circuit.
Monitoring open-circuit voltage.
Performing a controlled discharge.
Comparing retained capacity with the baseline.
Charge retention can support acceptance testing and state-of-health assessment.
Rate-capability testing assesses the effect of charge and discharge current on performance.
The programme can repeat capacity measurements at different:
Charge currents.
Discharge currents.
Temperatures.
Voltage limits.
States of charge.
The objective is to understand where increasing current reduces usable capacity, energy or voltage margin.
Thermal characterisation examines how battery performance changes across the relevant temperature range.
It can assess:
Capacity.
Energy.
Internal resistance.
Impedance.
Rate capability.
Voltage response.
Heating behaviour.
Charge acceptance.
Low-temperature limitations.
The test range should be linked to the mission, design limits and customer requirements. Generic room-temperature data are insufficient where the battery will operate across a materially different thermal range.
Cell electromotive force can be characterised using a slow charge and discharge at a controlled temperature with suitable relaxation periods.
ECSS-E-HB-20-02A describes a low-rate approach with measurements at defined capacity intervals and relaxation periods to approach steady-state conditions.
The resulting relationship can support understanding of cell voltage behaviour and state-of-charge estimation.
OCV-versus-state-of-charge mapping establishes the relationship between relaxed open-circuit voltage and available capacity under defined conditions.
It can support:
Battery-model inputs.
State-of-charge estimation.
Health-check methods.
Comparison between cells.
Assessment of ageing changes.
The relationship can be temperature- and history-dependent. It should not be treated as a universal or complete battery-management algorithm.
Characterisation should be repeated at defined programme points, such as:
Before environmental testing.
After vibration or shock.
After thermal-vacuum exposure.
During life testing.
After storage.
Before and after AIT.
Following an anomaly.
Consistent methods allow changes to be distinguished from normal measurement variation.
Insufficient sampling can hide cell-to-cell or lot-to-lot variation.
Testing only one cell may provide detailed data about that cell without establishing whether the result represents the production population.
Characterisation is often underestimated during programme planning.
Thermal stabilisation, conditioning cycles, rest periods, self-discharge tests and repeated measurements can require substantial time.
Repeating characterisation after a design, supplier, chemistry or manufacturing change can be expensive.
The greater cost, however, is proceeding into qualification with an invalid baseline.
Incorrect or inconsistent characterisation can undermine later qualification, acceptance and life-test conclusions.
Examples include:
Changing the charge method between tests.
Comparing results from different temperatures.
Using different cut-off voltages.
Failing to control rest periods.
Ignoring state of charge.
Using unrepresentative samples.
Omitting measurement uncertainty.
Losing test history.
Incomplete baseline data limit future comparison.
Missing raw data, sensor positions, sampling rates, calibration details or test conditions can make later trend analysis unreliable.
A correlation should not be presented as a proven degradation mechanism.
Capacity, resistance and impedance changes should be interpreted using appropriate electrochemical, thermal and mission context.
Characterisation involves stored electrical energy, charging, discharging and temperature exposure.
The programme requires:
Defined operating limits.
Abort criteria.
Safe electrical connections.
Temperature monitoring.
Hazard assessment.
Controlled charging.
Emergency response arrangements.
Avoid drawing population-level conclusions from a single sample.
Sample quantities should reflect:
Design variability.
Manufacturing variability.
Lot structure.
Test purpose.
Available heritage.
Programme risk.
Space batteries rarely operate only at room temperature.
Testing should cover the temperatures relevant to:
Charging.
Discharging.
Storage.
Contingency operation.
Qualification.
End-of-life assessment.
State of charge affects voltage, resistance, impedance, heating and safety behaviour.
Specify, verify and record it.
Use the same:
Charge protocol.
Voltage limits.
Rest periods.
Discharge conditions.
Temperature-control method.
Sampling approach.
Calculation method.
Consistency is essential when comparing results over time.
Retain voltage, current, temperature and time-history data alongside calculated results and plots.
Future investigations can depend upon information that was not considered important during the original test.
Characterisation should precede environmental and life testing.
Otherwise, later changes cannot be reliably distinguished from initial variation.
Use test results to challenge and update analytical predictions.
Do not adjust a model solely to fit one dataset without assessing whether it remains valid outside that test condition.
Maintain traceability of:
Cell activation.
Storage.
State of charge.
Conditioning.
Previous cycling.
Environmental exposure.
Transport.
Anomalies.
Configuration changes.
Independent review should challenge:
Sampling.
Test conditions.
Instrumentation.
Calculation methods.
Model assumptions.
Data exclusions.
Engineering conclusions.
Claims of representativeness
Defines how battery requirements will be verified using test, analysis, inspection or review of design.
Defines the objectives, samples, conditions, parameters, sequence, resources and data outputs.
Defines the controlled technical requirements, tolerances and success criteria.
Defines the execution steps, conditioning, measurements, hold points and anomaly responses.
Demonstrates that the test articles, equipment, procedure, safety controls and personnel are ready.
Records the configuration, methods, conditions, results, analysis, deviations and conclusions.
Contains the controlled voltage, current, temperature, time and other agreed measurement records.
Documents model structure, inputs, assumptions, limitations and correlation with test data.
Links requirements to verification methods, evidence and closure status.
Record anomalies, technical assessment, disposition and closure.
Defines storage, charging, maintenance, handling and operating conditions.
Identifies the approved dataset used for subsequent comparison, modelling and verification.
The required characterisation activities address approved project requirements or documented engineering objectives.
Measurements are complete, controlled, traceable and supported by suitable instrumentation.
Repeated tests under equivalent conditions produce results within the approved variation or uncertainty.
The approved baseline clearly identifies:
Test articles.
Configuration.
Conditions.
Measurement methods.
Raw data.
Calculations.
Limitations.
Measured behaviour is compared with analytical predictions, and material differences are investigated.
The evidence is sufficient for the conclusion being drawn. A small sample is not presented as proof of wider production consistency without justification.
The relationship between requirement, test article, procedure, instrumentation, raw data, calculation and conclusion is clear.
The evidence supports defined design, qualification, acceptance or life-test decisions.
Characterisation evidence contributes to customer or design-authority flight-readiness assessment.
It does not independently approve the battery for flight.
Resonate Testing can help translate battery, mission and verification requirements into a practical characterisation programme.
Our engineers can review:
Characterisation objectives.
Test-item configuration.
Sample quantities.
State-of-charge conditions.
Charge and discharge profiles.
Temperature conditions.
Instrumentation.
Data-acquisition requirements.
Reporting expectations.
Resonate can support coordinated battery characterisation and related environmental testing where the agreed scope, equipment capability and safety assessment permit.
The campaign can be structured to establish controlled measurements before and after relevant environmental exposure.
Support can include preparation or review of:
Test plans.
Test specifications.
Test procedures.
Test set-up records.
Characterisation reports.
Data packages.
Nonconformance evidence.
Independent review can identify:
Sampling weaknesses.
Uncontrolled assumptions.
Inconsistent measurement conditions.
Instrumentation gaps.
Missing traceability.
Overstated conclusions.
Evidence limitations.
Resonate generates controlled test evidence for customer review within wider qualification and flight-readiness processes.
All battery activity remains subject to:
Technical review.
Equipment suitability.
Test-item condition.
Hazard assessment.
Facility safety approval.
Schedule and resource availability.
Agreed commercial scope.
Confirmation of applicable accredited scope.
Resonate Testing does not:
Certify batteries as ECSS compliant.
Grant flight approval.
Replace the design authority.
Guarantee mission life.
Validate a complete battery model from limited data.
Provide every test described in ECSS guidance.
Assume that cell-level results prove complete battery behaviour.
Resonate Testing helps customers convert mission and verification requirements into controlled, traceable test evidence.
Your Test Facilitator. Not simply a test facility.
It is the controlled measurement of battery capacity, energy, resistance, impedance, charge retention, self-discharge, rate capability and other relevant performance parameters.
No.
Characterisation establishes how the battery behaves. Qualification demonstrates that a representative design satisfies approved requirements with the required qualification margins.
Characterisation data can support qualification but does not replace it.
The required activities depend on the project baseline, contract, battery design, verification plan and approved tailoring.
ECSS-E-HB-20-02A provides guidance on relevant tests. It does not make every activity universally mandatory.
Capacity is the electrical charge delivered and is normally expressed in ampere-hours.
Energy accounts for both current and voltage during discharge and is normally expressed in watt-hours.
Temperature affects capacity, energy, resistance, charge acceptance, voltage behaviour and rate capability.
A result obtained at room temperature may not represent performance at mission operating temperatures.
State of charge affects terminal voltage, internal resistance, impedance, heating and safety behaviour.
It must be specified and recorded for meaningful comparison.
There is no universal number.
The sample quantity should reflect the test objective, expected variability, manufacturing-lot structure, heritage and programme risk.
No.
One cell can provide information about that specific test article. A complete battery introduces electrical interconnections, thermal gradients, restraint, cell imbalance and protective devices.
Internal resistance helps explain voltage drop and heating under load. Changes can indicate altered battery performance.
It does not, by itself, prove a specific degradation mechanism.
It measures frequency-dependent impedance under controlled state-of-charge and temperature conditions.
The results can support comparison, modelling and ageing assessment, but interpretation requires suitable technical analysis.
Characterisation provides important inputs to life prediction.
Reliable mission-life prediction also requires representative ageing data, mission profiles, environmental conditions, validated models and stated uncertainty.
Typical points include before qualification, after significant environmental exposure, during life testing, after storage, before and after AIT, or following an anomaly.
It should identify the test article, configuration, history, conditions, methods, equipment, instrumentation, raw data, calculations, uncertainty where required, deviations, nonconformances and conclusions.
ECSS-E-HB-20-02A Lithium-Ion Battery Testing
ECSS Battery Qualification Testing
Battery Ageing and Life Testing Under ECSS
Space Battery Environmental Testing
Battery Safety and Abuse Testing
UN 38.3 Versus Space Qualification Testing
Lithium-Ion Battery Capacity and Energy Testing
Battery Internal Resistance Testing
Battery AC Impedance Testing
Battery Self-Discharge Testing
Battery Charge-Retention Testing
Battery Rate-Capability Testing
OCV Versus State-of-Charge Mapping
Vibration Testing Under ECSS
Shock Testing Under ECSS
Thermal Vacuum Testing Under ECSS
Battery Thermal Vacuum Testing
Battery Vibration and Shock Testing
Verification Planning
Verification Matrices
Verification Evidence
Requirements Traceability
Space Qualification Process
Verification Control Documents
Test Readiness Reviews
Battery Test Plans
Test Specifications
Test Procedures
Test Reports
Nonconformance Management
Battery characterisation is not simply a preliminary laboratory exercise.
It establishes the evidence needed to understand battery performance, challenge design assumptions, plan qualification, assess degradation and interpret later environmental or life-test results.
A weak baseline creates uncertainty throughout the programme. A controlled baseline gives engineers a defensible reference for every subsequent decision.
Resonate Testing helps customers plan and deliver controlled battery and environmental test campaigns supported by clear, traceable evidence.
Your Test Facilitator. Not simply a test facility.
Whether you’re looking to contact us for the first time or have another testing requirement, we’d love to hear from you.
