All materials are made up of atoms which come together in groups and form molecules. In a chemical reaction, the atoms of different molecules rearrange, and form new molecules. Sometimes when this happens, a part of the atom, the electron, is released and leaves the newly formed molecule. In a battery, two types of chemical reactions occur:
one that produces electrons
and
one that consumes electrons.

These reactions are connected by a wire so that the electrons from one reaction flow through the wire to the other reaction. This flow of electrons is called electricity and can be used to do useful work like charging a cell phone!

The two reactions are also connected by a salt solution (called an electrolyte solution), which allows charged atoms called ions to flow between the reactions. This flow of ions is needed, because the reactions cause charge to build up near the surfaces that must be balanced by opposite charges for the reaction to continue to happen.

So, to make a battery, you need to have two different reactions connected by an electrolyte solution. For example, a zinc coated nail and a copper coated penny inserted into a lemon gives you two reactions, one occurring at the surface of the nail, and one at the surface of the penny. The electrons transferring between these reactions gives you enough electricity to run an LED lightbulb!

Both apples and Canada Dry work as an electrolyte solution, but to produce power, you need two reactions to occur. So, you could try inserting a nail and a penny into the apple to see how an apple battery compares to a lemon battery!