Any fruit or vegetable can be used as long as it contains salty or acidic juices that can act as an electrolyte. In the case of mandarins and oranges, you need to poke the internal segments so the juices are in contact.
For electrodes, we use Australian $1 or $2 coins as they contain 92% copper. At the Zinc electrode, we use galvanised nails as these are zinc-plated.
Full instructions (4 pages) available as a download in Word format after purchase (sample page below).
The instructions describe how to make potato, lemon and salty-water batteries.
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