Internal Resistance
Definition
Total opposition to current flow within a battery cell, including ionic resistance in electrolyte and electronic resistance in electrodes and current collectors. Increases with age and low temperature.
Why It Matters
- Causes voltage drop under load (V = I × R)
- Generates heat during discharge (P = I² × R)
- Increases with cell aging (impedance rise)
- Higher at low temperature, limiting cold performance
Common Pitfalls
- Not measuring internal resistance at application temperature
- Ignoring frequency dependence (AC vs. DC resistance)
- Not tracking resistance increase as aging indicator
- Using single resistance value across full SOC range (varies)