Our copy of The Dangerous Book for Boys arrived and the kids have enjoyed it. Our first project we did out of the book was the battery:

Homemade battery.

Ten alternating layers of quarters, aluminum foil, and construction paper soaked in vinegar and salt got us five volts and enough power to light the LED. Note that if you leave the battery assembled overnight you get to give a little lesson in electroplating the next morning. You've been warned.