The complete build process for crystal power cells. 

Needed Items:

Solid magnesium rod.  Aluminum can also be used but will give a lower voltage.
Copper pipe cap.

Equal Parts of the following:
Potassium chloride - commonly known as salt substitute.
Hydrated potassium aluminium sulfate - commonly known as alum.
Sodium tetraborate - commonly known as 20 mule team Borax.
Magnesium sulfate - commonly known as epsom salt.

Reliance 9001829005 32-Inch Magnesium Water Heater Anode Rod

Price: $27.49

Link: http://www.amazon.com/gp/product/B003110YN8/

Great prices on magnesium here:  http://www.mcssl.com/store/gallium-source/magnesium-metal

Galvanic Chart: http://www.nordhavn.com/resources/tech/images/Galvanic_Series.pdf