Interesting site of engineering humor, jokes, trivia, puzzles. I liked this one (as quoted by J-Walk):
So, how many AA batteries would it take to power a standard adult human for one day?
A Manganese/Alkaline AA cell it rated at about 2.4 amp-hours. If we assume 1.5 volts average this gives approximately 3.6 watt-hours (slightly optimistic). Since there are 3,600 seconds in an hour this is equivalent to 12,960 Joules.
A human consumes about 2,000 calories/day. A dietician calorie is equal to 1,000 engineering calories. A calorie is equal to 4.2 Joules. Therefore this is equivalent to 2,000 * 1,000 * 4.2 = 8.4 * 106 Joules per day.
Dividing one by the other you will need about 648 AA cells to power a human for one day.
This assumes that the power from the AA cell will go through the same inefficiencies as the chemical processes in a human. (A human runs at about 20% efficiency chemical energy to mechanical energy). If we can circumvent this inefficiency we would only need 20% of this number of cells – say 130 cells.
Good thing to remember next time you swing past Costco.