Views: 0 Author: ZERNE Battery Technical Content Team Publish Time: 2026-09-18 Origin: Site
A battery pack may show the correct nominal voltage and capacity while still performing poorly during a high-current event. A short startup surge, motor load, wireless transmission burst or actuator movement can cause the pack voltage to fall below the device’s minimum input requirement.
A battery pack DC internal resistance test helps quantify this load response. Instead of measuring only the open-circuit voltage, the test applies a controlled current change and records the resulting voltage change at the battery terminals.
The measured result is not a universal property that can be compared without context. DC internal resistance changes with:
State of charge;
Battery temperature;
Rest time;
Pulse current;
Pulse duration;
Measurement location;
Cell configuration;
BMS behavior;
Connector and cable resistance;
Test equipment and wiring.
For OEM projects, the purpose of DCIR testing is therefore not simply to obtain one resistance number. The purpose is to create a repeatable method that helps engineers compare samples, identify production variation and confirm that the battery can support the actual device load.
A controlled DCIR test generally follows these steps:
Define the test objective and acceptance question.
Charge or discharge the battery to the required SOC.
Stabilize the battery at the specified temperature.
Allow the battery to rest for the defined period.
Measure the initial battery voltage and current.
Apply a controlled current pulse.
Record the voltage response and actual current change.
Calculate DCIR using the defined time point.
Repeat the measurement under the same conditions.
Compare the results with the approved sample or project-specific limits.
For a discharge pulse, a simplified calculation is:
RDC = ΔV ÷ ΔIWhere:
ΔV is the voltage drop caused by the current increase;
ΔI is the actual change in current;
RDC is the calculated DC internal resistance.
The test should use synchronized voltage and current data measured at appropriate battery terminals. Results should always be reported together with SOC, temperature, rest time, pulse profile and measurement method.
DC internal resistance describes how much the battery pack voltage changes when the current changes over a defined test interval.
During a discharge pulse, the pack voltage normally decreases as current increases. Some of this voltage change is related to the electrical resistance of the cells and the rest of the pack’s current path.
At pack level, the measured response may include:
Cell resistance;
Cell-to-cell variation;
Nickel strips or busbars;
Welds and terminals;
Fuse resistance;
BMS protection components;
Current-sensing elements;
Wires;
Connectors;
Contact resistance;
Temperature-dependent electrochemical effects.
This means that pack-level DCIR is not necessarily the same as the resistance of an individual cell.
The result also depends on the time point selected for the calculation. A voltage measured immediately after the current step may produce a different value from a voltage measured later during the same pulse. The test procedure should define whether the project is evaluating an immediate voltage step, a short-duration pulse response or a longer load event.
DCIR testing can support several OEM engineering decisions.
A battery pack with excessive resistance may experience significant voltage sag during a short high-current event. The device may reset, shut down or reduce performance even when the remaining capacity appears sufficient.
Testing several packs under the same conditions can reveal abnormal variation between samples or production batches.
An unusually high result may indicate a cell mismatch, weak connection, excessive contact resistance, incorrect wiring or a problem in the pack’s protection path.
DCIR results can help explain why a finished device performs differently from a laboratory capacity test. The actual device may have a strict minimum input voltage that is not visible in a simple capacity measurement.
Repeated measurements under controlled conditions can show how the resistance of a pack changes over time. A change in resistance should be evaluated together with capacity, temperature, protection behavior and physical condition.
The existing battery pack testing checklist covers the wider relationship between capacity, discharge, peak load, voltage sag, temperature and device-level validation.
The same battery pack may require different DCIR procedures for different engineering questions.
Test objective | Main question |
|---|---|
Design validation | Can the pack support the device’s expected peak load? |
Sample comparison | Which approved design provides the most stable load response? |
Incoming inspection | Does the received pack match the approved electrical behavior? |
Production control | Are pack results consistent across a batch? |
Troubleshooting | Is voltage sag caused by the battery, connector, BMS or device load? |
Aging study | How does the pack response change after repeated use? |
The objective determines the appropriate:
SOC points;
Temperature conditions;
Pulse current;
Pulse duration;
Number of repetitions;
Measurement locations;
Acceptance criteria.
A test designed for production screening may not be sufficient for detailed design validation. A short pulse used for incoming inspection may also fail to represent a motor startup event lasting several seconds.
A controlled battery pack DCIR test normally requires the following equipment.
The finished configuration should be tested, including the approved cells, BMS or PCM, fuse, wiring, connector, insulation and enclosure where applicable.
The load should be capable of producing the required current profile with controlled timing and repeatability.
Voltage should be measured at the defined battery terminals. When the project requires higher accuracy, separate sense leads can reduce the effect of current-carrying lead resistance.
The actual current should be recorded rather than relying only on the programmed load value. The programmed and measured current may differ because of equipment response, protection behavior or connection resistance.
Temperature sensors should be placed at relevant locations, such as:
Cell surface;
Cell group;
BMS;
Connector;
Cable terminal;
Enclosure surface.
Voltage, current and temperature should be recorded with synchronized timestamps. The sampling rate should be appropriate for the pulse duration and the response being evaluated.
The battery should be charged or discharged to the required SOC using equipment compatible with the approved pack and BMS.
A DCIR value without test conditions is difficult to interpret. The test method should define the following items before measurement.
Battery resistance can vary across the SOC range. The project may require one representative SOC point or several points, such as low, middle and high SOC.
If several SOC levels are tested, each level should have a defined conditioning method. The battery should not be assumed to be at the target SOC merely because the charger has stopped.
For illustration only, an engineering team might compare results at approximately 20%, 50% and 80% SOC. These values are examples of test points, not universal requirements.
Temperature can materially affect the measured response. Low-temperature testing may produce higher resistance, while warmer conditions may reduce resistance for some battery chemistries. The exact behavior depends on cell design, chemistry, SOC and test history.
The procedure should specify:
Ambient temperature;
Battery temperature;
Temperature stabilization method;
Sensor location;
Permitted temperature range;
Whether the pack is tested inside or outside the device enclosure.
The battery should rest after charging or discharging before the pulse is applied. Rest time allows transient voltage behavior to settle and makes comparisons more repeatable.
The required rest time depends on the test objective. A very short rest may retain effects from the preceding charge or discharge. An excessively long rest may no longer represent the operating condition that the device experiences.
The pulse should represent the electrical event being evaluated. It may be based on:
Device startup;
Motor acceleration;
Radio transmission;
Heating element activation;
Actuator movement;
Converter input demand;
Maximum continuous load.
The test should record both the initial current and the pulse current. The calculation should use the actual change in current.
Pulse duration must be stated clearly. A battery can respond differently to a short current step and a longer high-load event.
The procedure should specify:
Current rise time;
Pulse duration;
Number of pulses;
Time between pulses;
Recovery period;
Voltage sampling points.
The report should identify whether voltage is measured:
Directly at cell terminals;
At the BMS output;
At the battery connector;
At the end of the cable;
At the device input.
These measurement points do not produce identical results. For OEM device validation, measuring at the device-side input may be useful because it includes cable and connector voltage drop. For pack construction analysis, measurements at several points may help separate cell, BMS and wiring contributions.
For a discharge pulse, define:
Vbefore: battery voltage immediately before the pulse;
Vduring: battery voltage at the selected point during the pulse;
Ibefore: current immediately before the pulse;
Ipulse: current during the pulse.
Then:
ΔV = Vbefore − Vduring
ΔI = Ipulse − Ibefore
RDC = ΔV ÷ ΔIThe time point used for Vduring must be specified. For example, a project may define the voltage immediately after the current step, at a selected millisecond point, or at a defined point during a longer pulse.
The same calculation should be applied consistently across:
Samples;
Production batches;
Test stations;
Instruments;
SOC levels;
Temperature conditions.
The following example is for explaining the calculation method only:
Initial current: 1.2 A;
Pulse current: 6.2 A;
Initial terminal voltage: 3.82 V;
Voltage at the defined pulse time: 3.64 V.
Therefore:
ΔI = 6.2 A − 1.2 A = 5.0 A
ΔV = 3.82 V − 3.64 V = 0.18 V
RDC = 0.18 V ÷ 5.0 A = 0.036 ΩThe illustrative result is 36 mΩ.
This is not ZERNE production data, not a universal limit and not a recommended acceptance value. Actual limits must be established for the selected cell, pack configuration, BMS, device load and test method.
DCIR and AC impedance are related but not interchangeable.
An AC method applies a small alternating signal at a specified frequency and measures the electrical response. A DCIR method applies a current change or pulse and observes the voltage response over a defined time interval.
The readings may differ because they are influenced by:
Signal type;
Frequency;
Pulse duration;
SOC;
Temperature;
Rest time;
Measurement location;
Instrument algorithm;
Pack construction.
A supplier report should identify the method used. An AC resistance value should not be compared directly with a DCIR value as though both represented the same measurement.
For additional battery-specific background, ZERNE’s drone battery internal resistance article provides a different, drone-focused explanation. The present article focuses on controlled OEM battery-pack validation, test conditions and repeatability.
SOC and temperature should be treated as controlled variables rather than incidental details.
Two identical packs may produce different DCIR results if:
One pack is tested shortly after charging;
One pack has rested longer;
One pack is colder;
One pack has a different SOC;
One pack has experienced a different recent load;
One pack is measured at the cell terminals while another is measured at the connector.
When comparing production batches, the most reliable approach is to use the same:
Conditioning procedure;
SOC target;
Temperature range;
Rest time;
Pulse profile;
Fixture;
Instrument;
Calculation method.
If a project needs results across multiple temperatures or SOC levels, each condition should have its own reference data and acceptance criteria.
A finished battery pack contains several possible sources of voltage drop.
The total response may include:
Cell electrochemical response;
Cell-to-cell imbalance;
Interconnect resistance;
Weld or terminal resistance;
BMS conduction path;
Fuse resistance;
Cable resistance;
Connector contact resistance;
Protection-system response;
Measurement-lead effects.
This is why a cell may pass a standalone test while the completed pack produces excessive voltage sag.
For troubleshooting, engineers may measure at different locations to determine where the voltage drop occurs. However, the production acceptance method should define one primary measurement point so that batch results remain comparable.
There is no single DCIR limit that applies to every lithium-ion battery pack.
A suitable limit depends on:
Cell model;
Cell chemistry;
Series and parallel configuration;
Capacity;
Continuous current;
Peak current;
BMS design;
Cable and connector;
Device minimum input voltage;
Operating temperature;
Required service life;
Supplier process capability.
A practical OEM acceptance approach may combine several types of criteria:
Compare production packs with an approved sample tested under identical conditions.
Build a distribution from qualified samples rather than selecting an arbitrary resistance value.
Confirm that the voltage sag under the defined load remains above the device’s minimum input requirement.
Confirm that the pulse and repeated-load response do not create unacceptable temperature rise.
Investigate results that differ significantly from the established batch trend, even if they remain below a simple upper limit.
The final acceptance rule should be agreed before production testing begins. The supplier and OEM should also define how borderline results, repeated measurements and failed samples are handled.
DCIR testing can be used at different stages of production.
A sample of received packs may be tested to confirm that the supplied configuration matches the approved design.
Selected subassemblies or completed packs may be checked after cell connection, BMS integration or connector installation.
The finished pack can be tested with its final wiring, connector, insulation and enclosure.
Qualified production lots can be sampled periodically to monitor process consistency.
Each stage should have a defined purpose. A final pack test should not be replaced by a cell-only resistance measurement when the project requirement concerns the battery pack delivered to the device manufacturer.
A result taken at a different SOC, temperature or pulse duration should not be treated as directly comparable.
The load setting may not equal the actual current at the battery terminals. The calculation should use synchronized measured data.
Cell-terminal, BMS-output and device-input measurements include different parts of the electrical path.
If the battery is already supplying current before the pulse, ΔI should reflect the actual current change rather than only the final pulse value.
A report that states “35 mΩ” without SOC, temperature, rest time, pulse duration and measurement point is incomplete.
A pulse that does not represent the device’s actual load may produce a technically repeatable but practically irrelevant result.
One pack cannot demonstrate batch consistency. Sample quantity should be determined by the project’s quality plan.
DCIR does not replace capacity testing, charging validation, BMS protection testing, thermal evaluation, mechanical inspection or device-level testing.
A useful DCIR report should include:
Battery model;
Project number;
Sample serial number;
Cell model and batch;
Pack configuration;
BMS or PCM model;
Connector and cable configuration;
SOC;
Ambient temperature;
Battery temperature;
Rest time;
Initial current;
Pulse current;
Pulse duration;
Measurement location;
Voltage sampling points;
Test equipment;
Calibration status;
Raw voltage and current data;
Calculation formula;
Calculated DCIR;
Acceptance criteria;
Pass/fail result;
Deviations;
Operator and test date.
The report should preserve raw measurement data where possible. A single calculated value is less useful when engineers need to investigate an abnormal waveform or compare different time points.
A battery pack may pass a controlled laboratory DCIR test but still fail in the product.
Device-level validation should confirm:
Startup voltage;
Maximum-load voltage;
Minimum device input voltage;
Voltage at the device connector;
Device reset behavior;
Converter response;
Cable and connector temperature;
Battery temperature;
Runtime under realistic operation;
Recovery after a peak load.
The device should be tested under normal, maximum-load and repeated-use conditions where relevant. DCIR is most useful when connected to the device’s actual electrical requirements rather than treated as an isolated specification.
It is a controlled test that applies a defined current change to a battery pack and measures the resulting voltage response. The resistance is calculated from the voltage change divided by the current change.
For a discharge pulse, DCIR is calculated as ΔV ÷ ΔI, using the defined voltage and current measurement points. The test must specify the time point used for the voltage reading.
Battery resistance changes with state of charge and temperature. A result measured at a different SOC or temperature may not be directly comparable with another result.
No. AC resistance or impedance uses an alternating signal, while DCIR uses a controlled current change or pulse. The methods can produce different values and should not be compared without understanding the test conditions.
There is no universal limit. The appropriate range depends on the cell, pack configuration, current demand, device voltage requirement, temperature, BMS and approved production data.
No. DCIR should be combined with capacity, charging, protection, temperature, mechanical, insulation and device-level tests.
The measurement point depends on the engineering objective. Pack-terminal measurement evaluates the delivered pack path, while cell-terminal measurement may help investigate cell behavior. The production test method must define the location consistently.
The required sample quantity depends on the OEM quality plan, production volume, risk level and statistical objectives. One sample is generally insufficient to demonstrate batch consistency.
A battery pack DC internal resistance test is a useful OEM validation tool because it connects current demand with voltage response. However, the result is meaningful only when the test conditions are controlled and documented.
A reliable method should define:
SOC;
Temperature;
Rest time;
Pulse current;
Pulse duration;
Measurement location;
Voltage and current sampling points;
Calculation method;
Repeatability requirements;
Acceptance criteria.
DCIR should not be treated as a universal cell-quality number or a complete battery safety test. The most useful evaluation combines DCIR with voltage-sag testing, temperature monitoring, BMS verification, production traceability and testing in the finished device.
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