Internal Resistance: What It Tells About Battery Quality
A concise technical guide by Huawen New Power — how internal resistance (IR) impacts lithium battery performance, safety, and lifespan, and how professionals measure and manage it in custom battery packs.
What Is Internal Resistance?
Internal resistance (IR) is the opposition within a battery to the flow of electric current. Measured in milliohms (mΩ), IR determines how much voltage drops and how much heat is produced when current flows through the cell. Low IR means better efficiency and higher usable power under load.
Why Internal Resistance Matters
- Efficiency & Power Output: Lower IR lets the cell supply high currents with small voltage loss.
- Thermal Stability & Safety: High IR produces heat that accelerates aging and increases safety risks.
- Cycle Life: IR typically increases as cells age — monitoring IR predicts end-of-life.
- Pack Consistency: Mismatched IR between cells causes uneven charging and reduces pack life.
Table: How IR Affects Common Metrics
IR (mΩ) | Typical Impact | Applications Affected |
---|---|---|
<10 mΩ | Excellent high-rate performance, low heating | EVs, power tools, drones |
10–30 mΩ | Good balance of power and cost | ESS, e‑bikes, portable devices |
30–100 mΩ | Noticeable voltage sag under load | Consumer electronics |
>100 mΩ | Poor performance at high current | Not suitable for high-drain use |
How We Control and Test IR at Huawen New Power
- Cell Sourcing: Work with A-grade suppliers for tight IR specs.
- Cell Matching: Test and group by IR, capacity & voltage.
- Precision Welding: Weld carefully to minimize extra resistance.
- Aging & Testing: Verify IR stability over charge-discharge cycles.
Quick Visual: IR vs. Performance
As IR goes up, the ability to deliver current drops.
What IR Reveals About Manufacturing Quality
Two cells with identical capacity and voltage may perform very differently under load if their IR differs. Lower IR often indicates:
- Better material purity and uniform electrodes
- Precise manufacturing and consistent assembly
- Strict cell sorting and matching
Conclusion
Internal resistance is a practical, measurable metric that correlates strongly with battery performance, safety, and lifespan. As a purchaser or system designer, always ask your battery supplier for IR data and matching tolerances.