Here is a cool Do It Yourself article from Instructables. This guide will show you how you can create a battery yourself with the ordinary household items. The comment on the article says that the power of the cell will be nearly 0.5V. But you can change the electrolyte solution to more acidic to get more power, also can connect many cells together too.
The things you need to have
Water
Carbon Rod – The article will also show how you can get one from non alkaline battery.
Zinc strip (Foil can be used instead too)
Wires
Empty spice container
Hot Glue gun
Salt
Something small powered by small batteries
Read more here. Make sure that you read the comment section too.