Lemon powered battery

http://www.flickr.com/photos/visualdensity/ / CC BY 2.0

I remember in science class that you can create a rudimentary battery using citrus fruit, but I didn't remember the experiment until I saw the project linked below. It's a great way to explain and demonstrate how batteries and electricity works to kids!
http://www.mnn.com/family/education-activities/blogs/how-to-make-a-lemon-battery