cells
internal resistance
All you need is a 4 ohm 5W power resistor or similar and a multimeter.
- First, measure the battery's voltage when charged. This is V1
- Next, connect your multimeter leads to each side of the resistor and briefly connect the resistor across the battery. Note the voltage reading, this is V2.
- Measure your resistor to get its precise resistance, this is R
The battery's internal resistance (Ri) is calculated with the formula:
Ri = (V1-V2)*R/V2
18650 Ri values:
- 75-150 mOhm - Excellent
- 150-250 mOhm - Good
- 250-350 mOhm - Marginal
- 350-Up mOhm - Bad