Unveiling Battery Internal Resistance: Bigger or Smaller—Which Is Better?

In today’s rapidly developing technology, batteries have become an indispensable power source in our daily lives. Battery performance directly affects our experience of use, and among the many indicators used to evaluate battery performance, whether it is an 18650 battery or a 21700 lithium-ion battery, internal resistance (IR) is a crucial parameter. But the question is – is the higher the internal resistance, the better, or should it be as low as possible? Let’s uncover this mystery.

1. What Is Battery Internal Resistance?

Before diving into whether a higher or lower internal resistance is preferable, let’s first define what battery internal resistance actually is. Simply put, internal resistance refers to the opposition to current flow within the battery itself. This resistance arises due to the battery’s internal materials, structure, and chemical reactions. The magnitude of internal resistance directly affects power output, efficiency, and battery lifespan.

2. What Happens If Internal Resistance Is High?

A high internal resistance has several noticeable effects on a battery’s performance:

Reduced Efficiency:
Higher internal resistance means the battery must overcome greater resistance when discharging, leading to decreased effective power output and lower energy conversion efficiency.

Increased Heat Generation:
When a battery has high internal resistance, more heat is generated during charging and discharging. This accelerates battery aging and could pose safety risks such as overheating or thermal runaway.

Decreased Performance:
For applications that require high power delivery and rapid charge/discharge cycles—such as electric vehicles (EVs), drones, and power tools—a higher internal resistance can severely limit performance, reducing responsiveness and runtime.

3. What Are the Advantages of Low Internal Resistance?

Improved Efficiency:
A battery with low internal resistance minimizes energy losses, allowing for higher energy conversion and better overall performance.

Lower Heat Generation:
Reduced resistance means less heat is produced during operation, helping to extend battery lifespan and improve safety.

Enhanced Performance:
Batteries with lower internal resistance can provide higher power output and maintain voltage stability under heavy loads, making them ideal for high-power applications like EVs and industrial machinery.

4. Choosing the Right Battery: Does Internal Resistance Always Matter?

From the above analysis, a lower internal resistance generally means better battery performance. However, this does not mean internal resistance should always be as low as possible. Reducing internal resistance often comes at a trade-off, such as higher manufacturing costs or compromises in battery safety and lifespan.

• For applications that demand high efficiency and long lifespan, such as electric vehicles, batteries with low internal resistance are the best choice.
• For cost-sensitive applications where performance demands are lower, slightly higher internal resistance can be acceptable to reduce manufacturing costs.

In short, the ideal battery internal resistance depends on the intended use case.

5. Common Internal Resistance of Different Lithium Batteries

Each battery chemistry has its own advantages and trade-offs, with LFP batteries generally having higher internal resistance than NCM/NCA batteries but offering greater safety and longevity.

Conclusion

Is higher or lower battery internal resistance better? The answer depends on application-specific requirements. Lower internal resistance is preferred for high-performance applications where power efficiency, longevity, and responsiveness are crucial. However, in applications where cost savings matter more than performance, slightly higher internal resistance may be acceptable.

By understanding internal resistance, users can make more informed decisions when selecting batteries, ensuring they maximize performance while balancing factors like safety, efficiency, and longevity.