Entering Electrochemistry | How to Accurately Measure of Battery Direct Current Internal Resistance(DCIR)

1. Perface

DCIR (Direct Current Internal Resistance) is the total internal resistance of a lithium-ion battery, calculated using Ohm’s Law from the voltage response to a applied current pulse: \(R = \Delta V / \Delta I\). DCIR measurement quantifies a battery’s ohmic resistance and polarization resistance in a single test, making it the most widely used method for evaluating power capability, state of health (SOH), and production consistency across the battery lifecycle — from R&D through manufacturing and field deployment. Standard DCIR test procedures are defined in IEC 61960, GB/T 31486, and the USABC HPPC manual, each specifying different pulse durations and application scopes.

2. What is DCIR in Battery?

Direct Current Internal Resistance (DCIR) measurement refers to the process of applying a direct current step signal to a battery and calculating the resulting resistance from Ohm’s Law based on the measured voltage change. It represents the total internal impedance of a battery, encompassing both ohmic resistance and polarization resistance. As a core component of new energy vehicles, energy storage systems, and consumer electronics, battery performance and safety have always been key concerns in the industry. Internal resistance is one of the most commonly used and intuitive performance parameters in battery testing. It is closely related to a battery’s power characteristics and energy efficiency, and provides critical references for lifespan prediction and safety assessment.

This article demonstrates how to conduct internal resistance testing using IEST’s high-precision charge-discharge equipment in accordance with the IEC 61960 international standard, and walks through the actual testing process via software configuration steps.

3. Why is DCIR Testing So Important?

DCIR testing is a core evaluation method that spans the entire battery lifecycle — from laboratory development and production line screening to end-use monitoring — because it simultaneously reflects power capability, aging state, and internal defect status.

3.1 DCIR: The “Blood Pressure Monitor” for Battery State of Health (SOH)

State of Health (SOH) is defined as the ratio of a battery’s current capacity or power capability to its rated value at beginning of life, expressed as a percentage. The gradual increase of internal resistance is a direct quantitative indicator of battery aging: it reflects internal degradation such as loss of active material, electrolyte decomposition, and SEI layer growth. By periodically monitoring these resistance changes, engineers can accurately assess battery SOH and predict remaining useful life, much like how tracking blood pressure reveals cardiovascular health trends.

3.2 DCIR: The “Throttle Response” Gauge for Power Performance

Internal resistance directly determines the battery’s voltage drop under high current (\(V_{drop} = I \times R\)). A lower internal resistance means less voltage sag, enabling stronger acceleration, faster charging, and reliable high-power output. DCIR is therefore a key metric for evaluating whether a battery cell can meet the peak power demands of applications such as electric vehicles and power tools.

3.3 DCIR: An Early “Smoke Alarm” for Battery Safety

Thermal runaway refers to an uncontrolled self-heating process triggered when internal heat generation exceeds the battery’s ability to dissipate it, potentially leading to fire or explosion. According to Joule’s Law (Q = I²Rt), abnormal internal resistance leads to excessive heat generation, increasing thermal runaway risk. Internal resistance testing can effectively screen out cells with internal defects such as micro-shorts, poor welds, or electrolyte dry-out, serving as a critical non-destructive safety inspection before batteries enter service.

3.4 DCIR: The Foundational “GPS Signal” for BMS Algorithms

A Battery Management System (BMS) is the electronic control unit responsible for monitoring, protecting, and optimizing battery pack operation, including SOC estimation, power limit enforcement, and cell balancing. An accurate internal resistance value is essential for the BMS to make correct decisions. It is crucial for precise State of Charge (SOC) estimation, real-time calculation of charge/discharge power limits, and implementing effective cell balancing strategies. Inconsistent internal resistance within a pack can severely compromise overall performance and lifespan.

3.5 DCIR: The “Quality Gatekeeper” in Production and Consistency Screening

On the production line, DCIR testing serves as a 100% inspection tool. It quickly identifies manufacturing flaws such as poor tab welding or insufficient electrolyte wetting. More importantly, DCIR measurement is the primary method for grading and matching cells with consistent internal resistance — the cornerstone of building high-performance, long-life battery packs.

4. Basic Principle of DCIR Measurement

DCIR measurement relies on the current pulse method: a defined current pulse is applied to the battery, the instantaneous voltage response is captured at high speed, and internal resistance is calculated from the ratio of voltage change to current change.

• Apply a constant current pulse to the battery.

• Record the instantaneous change in battery voltage.

• Calculate internal resistance using the formula:

\[ R = \Delta V / \Delta I \]

Where:

\(\Delta V\) = Voltage difference before and after the current pulse

\(\Delta I\) = Magnitude of the pulse current

The IEST ERT/ECT Series achieves voltage and current measurement accuracy up to 0.01% and supports 100 Hz high-speed sampling. This enables precise control of pulse signals and efficient, reliable acquisition of the millisecond-level voltage data on which accurate DCIR calculation depends.

5. Comparison of Major DCIR Testing Standards

DCIR measurement must be performed under a defined standard to ensure that results are comparable across laboratories, instruments, and time points. Different standards — IEC, GB/T, and USABC — vary in pulse duration, test conditions, and application focus due to regional regulatory requirements and target application fields. Understanding these differences ensures test results are comparable and reproducible, and is the foundation for meeting specific market access requirements or customer technical specifications.

The table below compares the core stipulations of three widely used standards. Notably, the IEC 61960 standard employs both a primary 10-second pulse and a shorter 1-second pulse — a dual-pulse methodology that separates ohmic resistance and polarization resistance components that manifest over different timescales, providing richer data for in-depth performance analysis.

Table 1: Comparison of Key International Standards for DCIR Testing of Lithium-ion Batteries.

Standard	Primary Scope / Application Field	Key Pulse Duration	Core Methodology & Purpose
IEC 61960	Portable Electronics (International Benchmark)	10s (Long) & 1s (Short)	Constant current pulse method. Uses two pulses to separate ohmic and polarization resistance for basic performance evaluation.
GB/T 31486	EV Power Batteries (China Market Access)	Typically 10s	HPPC or constant current pulse. Mandatory for safety & performance certification, with a strong focus on power capability.
USABC Manual	EV/HEV Traction Batteries (North America)	10s (within HPPC profile)	Hybrid Pulse Power Characterization (HPPC). Assesses peak power, available energy, and thermal management needs comprehensively.

The following illustrates the standard step sequence for IEC 61960 DCIR testing on the IEST ECT/ERT Series, consisting of three sequential phases that together capture both long-timescale and short-timescale resistance components.

Figure 1. Step-by-step DCIR test procedure flowchart following IEC61960 standard on IEST ECT & ERT Series Products

6.1 Rest Phase

• Purpose: Ensure the battery reaches a stable open-circuit voltage (OCV) state.

• Function: Eliminate electrochemical disturbances from previous charge or discharge operations before the DCIR measurement begins.

6.2 Constant Current Discharge Pulse (0.2C, 10s)

• Apply a constant current pulse at 0.2C rate for 10 seconds.

• Record the instantaneous voltage drop (IR drop) and its subsequent gradual stabilization during the pulse.

• This 10-second pulse is the primary data source for DCIR calculation per IEC 61960.

6.3 Short Pulse Verification (0.2C, 1s)

• Apply a shorter 1-second pulse at the same 0.2C rate to capture the faster voltage response component.

• The 1-second measurement isolates the ohmic resistance component from the slower polarization contribution captured in the 10-second pulse.

• Comparing both results enables a more complete internal resistance model.

Figure 2. Automatic DCIR Calculation and Export – IEST Analyzer Software

7. IEST ERT/ECT Series: Key Capabilities for Accurate DCIR Testing

The IEST ERT/ECT Series DCIR tester is designed to address the core accuracy, flexibility, and safety requirements of DCIR measurement across R&D, certification, and production quality control environments.

7.1 High-Precision Sampling

• Voltage measurement accuracy to microvolt level, ensuring capture of the instantaneous IR drop at the moment of current pulse application.

• 100 Hz high-speed sampling rate and stable current control for accurate pulse delivery and reliable DCIR calculation.

7.2 Flexible Step Design

• Supports rate-based modes (e.g., 0.2C, 0.5C), enabling DCIR tester configuration for batteries across a wide capacity range without manual current recalculation.

• Users can quickly configure test steps based on IEC 61960, GB/T 31486, or custom internal specifications, and save step templates for repeated use across batches.

7.3 Powerful Data Processing Capability

• Automatically calculates battery internal resistance, reducing manual analysis errors.

• Supports data export for further modeling and analysis.

7.4 Compliance with International Standards

• Fully compatible with IEC 61960, GB/T 31486, and USABC HPPC test methodologies.

• Suitable for various applications including research, certification, and quality inspection.

7.5 Safety Protection Mechanisms

• Built-in overvoltage, overcurrent, and overtemperature protection on all channels.

• Ensures safety for both the test instrument and the battery under test during high-current pulse operation.

8. Application Scenarios

IEST ERT/ECT Series DCIR testing solutions are deployed across multiple application environments:

• Power Battery R&D: Analyze the impact of different cathode and anode material systems on internal resistance at the cell level.

• Production Quality Inspection: Perform 100% DCIR screening to identify cells with abnormal internal resistance and improve pack-level consistency.

• Energy Storage System Validation: Monitor internal resistance changes in large-format storage batteries over cycling to detect aging trends before failures occur.

• Research Experiments: Combine DCIR measurement with EIS, cyclic voltammetry (CV), and rate capability tests to build comprehensive electrochemical models.

9. Summary

In practical terms, DCIR functions as a “cardiovascular health check” for batteries:

• The internal resistance value is akin to blood vessel patency (resistance). Low resistance means smooth blood (current) flow and strong pumping capacity of the heart (battery).

• Changes in internal resistance reflect aging and pathological changes (degradation and defects).

By tracking DCIR, engineers can assess power performance, quantify SOH, and identify safety risks — then act on that information through BMS management strategies or cell replacement decisions.

Throughout the entire battery lifecycle — from electrode material R&D and cell formation through production-line grading, pack assembly, and field monitoring — DCIR testing remains the most operationally practical and data-efficient method for evaluating battery performance, health, and safety. Accurate DCIR measurement requires a dedicated DCIR tester with millisecond-level sampling capability, calibrated current pulse control, and compliance with the applicable test standard (IEC 61960, GB/T 31486, or USABC). These requirements are the baseline for producing the resistance data that is reproducible across instruments, operators, and laboratories.

To learn more about high-precision DCIR testing solutions, contact IEST Instrument for technical consultation and equipment specifications.

10. FAQ About DCIR Test