Lemons are generally the best fruits for conducting electricity. The high acid content in these and other citrus fruits, such as oranges and limes, makes them superior conductors. Since lemons have more acid than other citrus fruits, they are usually the best conductors.
Choosing the right individual fruit also has an effect on its ability to conduct electricity. Lemons with more juice are better conductors because they allow for a freer exchange of electrons. A ripe, juicy lemon is better for making a battery than an unripe one with dry pulp. Overripe lemons lose some of their citric acid content, making them less well-suited for conducting electricity.