by Chase Wu
March 20, 2025
Battery industry, Battery knowledge, Battery materials
06 mins

Battery internal resistance – comprehensive analysis and optimization solutions

Battery internal resistance is an important parameter that affects battery performance. It determines the battery’s energy conversion efficiency, discharge capacity, and service life. In industries such as electric vehicles and battery energy storage systems, battery internal resistance directly affects overall energy efficiency, endurance, and safety. Therefore, understanding the source, impact, measurement and optimization methods of battery internal resistance is crucial to improving battery performance.

What is battery internal resistance?

Definition of internal resistance of a battery

Battery internal resistance refers to the resistance of the battery to the flow of current. It includes the combined resistance of components such as battery materials, electrodes, and electrolytes (find the top 10 lithium ion battery electrolyte manufacturer). Lower internal resistance means better current transmission efficiency, while higher internal resistance will lead to energy loss and heating problems. The battery internal resistance is usually measured in milliohms (mΩ), and measurement methods include AC impedance measurement (EIS), DC voltage drop method, LCR meter test, etc.

Classification of battery internal resistance

Ohmic resistance: determined by the electrodes, electrolyte, conductive materials, etc. inside the battery, mainly affecting the instantaneous voltage drop.
Polarization resistance: the resistance caused by electrochemical reactions during the battery’s charge and discharge process affects the dynamic performance of the battery.
AC and DC internal resistance: AC internal resistance is usually used to evaluate short-term impedance, while DC internal resistance is closer to the battery performance under actual working conditions.

Factors affecting battery internal resistance

Temperature: high temperature will reduce internal resistance, but may accelerate battery aging, while low temperature will increase internal resistance and affect discharge performance.
Charge and discharge state: the state of charge (SOC) will affect the internal resistance. Usually, the internal resistance is low in the medium SOC range, and high in the low or full power state.
Battery aging: as the number of cycles increases, material changes and side reactions inside the battery will increase the internal resistance and affect performance.

What impact will the internal resistance of the battery make?

Impact on battery cycle life

Higher internal resistance will cause the battery to generate more heat during use, accelerate battery aging, and shorten service life.

Impact on battery performance

Voltage drop: Increased internal resistance will cause a greater voltage drop, which will affect the battery output power.
Heat generation: Higher internal resistance will cause greater energy loss, increase battery temperature, and may even cause thermal runaway.

Impact on electric vehicles and energy storage systems

In the field of electric vehicles, high internal resistance may lead to reduced acceleration performance and reduced endurance. In energy storage systems, high internal resistance will affect energy conversion efficiency and long-term stability.

How to measure the internal resistance of the battery?

Common methods for measuring battery resistance

DC discharge internal resistance measurement method

Measure the voltage drop during large current discharge, which is suitable for rapid detection in practical applications. Specific
The internal resistance is calculated by applying a large current (40A-80A) for a short time (2-3 seconds) and measuring the voltage across the battery. This method has high accuracy (the error can be controlled within 0.1%), but it is easily affected by polarization and may damage the battery, so it is suitable for large-capacity batteries.

AC voltage drop internal resistance measurement method

The impedance characteristics of the battery are tested by AC signals of different frequencies, which is suitable for laboratory research. Specifically, a fixed frequency (such as 1kHz) and a small current (50mA) are used to measure the impedance of the battery. This method has a very short measurement time (about 100ms) and is suitable for all types of batteries, but it is easily affected by ripple current and harmonic interference, which tests the anti-interference ability of the measuring equipment.

In addition, LCR meters and special internal resistance testers, which can be used for production and quality inspection.

Method to calculate internal resistance of battery

Calculation according to the R=U/I formula:

Measure the open circuit voltage U1.
Discharge with a fixed resistor R in parallel.
Record the battery voltage U2 after discharge.
Calculate the internal resistance: r = (U1 – U2) / (U2 / R). For example, if U1 = 12V, U2 = 10V, and the parallel resistance R = 10Ω, then r = (12-10) / (10/10) = 2Ω.

Generally speaking, the greater the internal resistance, the worse the battery’s load capacity. High-power batteries (such as power batteries) have a smaller internal resistance, while low-power batteries (such as 9V batteries) have a relatively large internal resistance. Reasonable measurement and optimization of internal resistance are essential to improving battery performance and service life.

Methods for reducing battery internal resistance

The internal resistance of lithium batteries directly affects their charge and discharge performance, energy conversion efficiency, and service life. To reduce internal resistance and improve battery performance, the following measures can be taken:

Optimize electrode materials: Use highly conductive, porous or nanostructured electrode materials to improve the transmission efficiency of electrons and ions and reduce ohmic internal resistance.
Increase electrolyte ion conductivity: Select an electrolyte with high conductivity, or add special additives to improve ion migration. At the same time, the application of solid electrolytes can also reduce internal resistance.
Improve diaphragm performance: Optimize diaphragm structure, such as increasing porosity or using multi-layer diaphragms to reduce ion transmission resistance.
Control temperature: Maintain the battery within the optimal operating temperature range through an efficient thermal management system to reduce the increase in internal resistance caused by temperature changes.
Optimize battery structure design: Use stacked structure, reduce pole piece thickness, optimize pole ear design, etc. to shorten the current path and reduce contact resistance.
Optimize battery management system (BMS): Through intelligent management, control the operating temperature and charge and discharge state of the battery to reduce the growth of internal resistance.

Comparison of battery internal resistance in different types of batteries

Lithium-ion battery vs. lead-acid battery

Comparison between lithium-ion battery vs lead-acid, lithium-ion battery has lower internal resistance and higher energy conversion efficiency, while lead-acid battery has higher internal resistance, resulting in weaker power output.

Different chemical systems (NCM, LFP)

Lithium iron phosphate (LFP) batteries usually have higher internal resistance than ternary lithium (NCM), but better safety.

Impact of battery aging

Different battery types have different internal resistance growth trends after cyclic use. The internal resistance growth rate of NCM batteries is usually faster, while LFP batteries are more stable.

Conclusion

Battery internal resistance has an important impact on battery performance, life and application scenarios. By optimizing materials, improving manufacturing processes, and strengthening battery management, the internal resistance can be effectively reduced and the overall energy efficiency of the battery can be improved.

With the advancement of battery technology, future batteries will make greater breakthroughs in internal resistance control, thereby improving the performance and reliability of electric vehicles and energy storage systems.

FAQ

What is the average internal resistance of a battery?

The internal resistance of a battery varies significantly depending on its type, size, materials, and design. Here are typical ranges for common battery types:
Lead-acid batteries: Generally below 10 milliohms (mΩ), with high-quality ones as low as 6 mΩ
Lithium-ion batteries: Standard types (e.g., 18650): 12–30 mΩ for high-performance models, and up to 50 mΩ for general-purpose cells .
Power-type lithium batteries (used in EVs): Often below 15 mΩ to support high discharge currents .
Nickel-cadmium (NiCd) batteries: Extremely low internal resistance (similar to lead-acid), enabling rapid charging and high-current discharge .
Nickel-metal hydride (NiMH) batteries: Slightly higher than NiCd, typically 20–50 mΩ .
Hydrogen-oxygen fuel cells (now obsolete): Exceptionally low initial resistance (~10 mΩ), decreasing further during discharge .

How to reduce internal resistance of battery?

1. Material-Level Improvements

Use high-conductivity electrode materials (e.g., silicon-carbon composites, high-nickel ternary materials).
Employ low-viscosity electrolytes for better ion mobility.
Optimize separator thickness and porosity to minimize ion transport resistance.

2. Design and Manufacturing Enhancements

Increase the number of electrode tabs and shorten the current path.
Improve electrode uniformity with advanced coating and calendaring techniques.
Utilize laser welding for tighter connections and lower contact resistance.

3. Thermal Management

Maintain an optimal operating temperature (20–40°C) to improve electrolyte conductivity and reduce polarization resistance.

Which battery has lowest internal resistance?

Lithium-ion batteries

Modern lithium iron phosphate (LFP) and high-performance lithium-polymer batteries exhibit the lowest resistance (as low as 6–12 mΩ), making them ideal for high-power applications like electric vehicles .
Nickel-cadmium (NiCd) batteries

Historically known for ultra-low resistance (~10 mΩ), suitable for tools and aviation despite environmental concerns .
Hydrogen-oxygen fuel cells

Achieved <10 mΩ but faced safety and cost challenges.

Chase Wu

Hello, I'm Chase. I specialize in providing in-depth insights and the latest updates on electric two- and three-wheeler battery swap systems, from lithium battery technology to intelligent swapping solutions. My goal is to break down complex technical concepts into clear, accessible content, helping businesses and individuals navigate the evolving landscape of electric mobility and sustainable energy.

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