Measuring Internal Resistance of Batteries

Contributors: Shawn Hymel
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Calculate the Internal Resistance

Using the voltage readings from the "10k Ω Load" and the "No Load" (open circuit), calculate the internal resistance of the lemon battery.

Hint: Refer to the Internal Resistance section to see how to calculate this value.


  1. Does the internal resistance of the lemon battery seem high or low?
  2. What is the maximum current your lemon battery can provide? (Hint: imagine connecting a wire between the terminals. How much current would flow through the circuit?)
  3. Re-calculate the internal resistance using the "330 Ω Load" and "No Load" values. Does it match your first calculation? If not, what do you think would cause the difference?
  4. Perform the whole experiment again using a consumer-grade battery, such as a AA alkaline cell. What is the maximum current a AA can provide?