Battery Internal Resistance Calculator
Calculate battery internal resistance from open-circuit and loaded voltage measurements, determine power loss and maximum short-circuit current.
Formula
R_{int} = \frac{V_{ocv} - V_{load}}{I_{load}}
How It Works
Battery internal resistance is a critical parameter that measures the opposition to current flow within a battery, directly impacting its performance and efficiency. The internal resistance (Rint) represents the inherent electrical resistance of the battery's chemical components, including electrolyte, electrodes, and connections. As a battery ages or experiences different environmental conditions, its internal resistance can change, affecting power delivery, voltage drop, and overall energy efficiency.
Worked Example
Problem: A lithium-ion battery with an open-circuit voltage of 4.2V shows a load voltage of 3.9V when delivering 2A. Calculate the battery's internal resistance and power loss. Solution: 1. Calculate Internal Resistance: Rint = (Vocv - Vload) / IL 2. Vocv = 4.2V, Vload = 3.9V, IL = 2A 3. Rint = (4.2V - 3.9V) / 2A = 0.15Ω or 150mΩ 4. Power Loss: Ploss = IL² × Rint = (2A)² × 0.15Ω = 0.6W 5. Efficiency = (3.9V / 4.2V) × 100% = 92.86%
Practical Tips
- ✓Measure internal resistance periodically to track battery health
- ✓Avoid deep discharge cycles to minimize resistance increase
- ✓Use temperature-compensated measurements for more accurate results
Common Mistakes
- ✗Neglecting temperature effects on internal resistance
- ✗Assuming constant internal resistance throughout battery life
- ✗Not considering battery chemistry differences in resistance values
Frequently Asked Questions
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