This is a derivation of brenn10's battery based on a comment by westfw, mainly because I wanted to see if it would work.

Either watch a lame video, of continue reading.

Step 1: Wacha Wacha Gonna Need?

sandpaper
post 1982 pennies
wire & solder
soldering iron
cardboard
lemon juice
led

Step 2: Prep the Pennies

Sand one face off each penny to expose the zinc core. Using 220 grit and holding in my fingers, it took about 45 secs of sanding to do each penny.

Alternately I tried both belt sander and disk sander, excellent ways to burn your fingers, but not appreciably faster.

Step 3: The Electrolyte

Cut up some cardboard from the back of a notebook and soak it in lemon juice, then blot dry.

Step 4: Assemble

pick out two pennies and solder leads to one face on each of them, one with the lead on the copper face, the other with it on the zinc face.

Now start stacking coins and cardboard, with all the coins copper side up, stack them with a peice of soaked cardboard between, secure with a rubber band and attach the leads to a low current electrical device, the copper side is the positive. And Tool said "Let there be light".