Measuring Internal Resistance of Batteries

Contributors: Shawn Hymel
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Build a Lemon Battery

We get to build a battery! This is a crude fruit-based battery that will not last very long nor drive much current. However, it is useful for measuring internal resistance.

IMPORTANT: Please don't eat the fruit after you have made the battery! Zinc ions that are floating in the lemon juice certainly can't be healthy for you.

Insert the zinc screw or nail into one side of the lemon.

Make the anode in the lemon battery

Use the hobby knife to cut a slit in the other end of the lemon.

Cut a slit for the penny

Insert a penny into the slit so that half of the penny is still outside the lemon's skin.

Insert penny to make the cathode

And that's it! We successfully created a battery. Make sure that the penny and screw cannot touch each other, or you will create a short circuit between the electrodes. While the short circuit will not start any fires, it will not produce a voltage for our experiments.

NOTE: If you would like the battery to last longer than a few hours, remove the screw. Even without a circuit connected, the screw will continue to oxidize in the presence of the lemon juice.