EUDAX Fruit Battery Science Experiment Kit-$7.99

If you have a budding scientist or engineer at home, here is a fun DIY teaching toy that can start them on a path toward understanding electrochemistry. The kit includes four pieces of copper sheet, four pieces of wire, two pieces of wire with clips, an electronic clock, and two light-emitting diodes (LEDs). Fruits, vegetables, or beverages such as apples, oranges, potatoes, lemons, tomatoes, cola, pears, pineapples, or salt solutions can be used with the copper electrodes to assemble a battery to power the included electronic clock or LED lights.

Available at a variety of places online, including Amazon.