1. What is Battery Internal Resistance?

Internal resistance is the opposition to the flow of current within a battery, causing voltage drop under load. It's a key indicator of battery health and performance.

2. How Does the Calculator Work?

The calculator uses the internal resistance formula:

Where:

• \( r \) — Internal resistance (Ω)
• \( V_{oc} \) — Open circuit voltage (V)
• \( V_{load} \) — Voltage under load (V)
• \( I \) — Current (A)

Explanation: The voltage difference between no-load and loaded conditions divided by the current gives the internal resistance.

3. Importance of Internal Resistance

Details: Lower internal resistance means better battery performance, higher efficiency, and less voltage drop under load. As batteries age, internal resistance increases.

4. Using the Calculator

Tips: Measure V_oc with no load, then measure V_load and current under a known load. All values must be positive and current must be greater than zero.

5. Frequently Asked Questions (FAQ)

Q1: What's a typical internal resistance value?
A: Varies by battery type and size. For AA alkaline, typically 0.1-0.3Ω when new. Lithium-ion may be 0.05-0.1Ω per cell.

Q2: How does temperature affect internal resistance?
A: Resistance increases at lower temperatures and decreases at higher temperatures (within safe operating range).

Q3: Why measure internal resistance?
A: It's a good indicator of battery state-of-health. Increasing resistance often precedes capacity loss.

Q4: Can internal resistance predict remaining capacity?
A: Indirectly. While no direct correlation, significant resistance increase usually indicates aging and reduced capacity.

Q5: How accurate is this calculation?
A: Provides a good estimate. For most accurate results, use a proper battery tester that measures at multiple current levels.