The average mobile phone battery stores about 10-20 thousand joules,
not 3-4 joules as I said before…eg my n73 battery is
3.7 Volts x 1000 mAmp-hours = 3.7 Watt-hours = 13,200 Joules..

So to produce enough energy to recharge it with foot power
would take about 5 minutes of pumping … eg 40 Watts x
300 seconds = 12,000 Joules.

Ken

Energy is not measured in Watts…power is! Power is the rate at which energy is used.
Energy is measured in Joules (or kilojoules, or watt-hours, or watt-seconds).

If 1 joule of energy is used in 1 second, then the power rate is 1 watt…if 1 joule is used in 1/1000 of a second,
then power is being used at the rate of 1000 watts.

Electrical devices are usually rated in watts, but to calculate how much energy they use you have to multiply by how long they are used. For example a smallish TV set might be rated at 100 watts. That means it uses energy at the rate of 100 joules per second. If you run it for an hour, then it uses 100×60x60 joules, which is also know as 100 watt-hours, and will probably appear on your energy bill as 0.1 kilowatt-hours.

People are very low producers of power. The average fit person can generate power at the rate of 75-100 watts for about 8 hours before becoming exhausted. That means, if you pump this device continuously for 8 hours, you have generated enough energy to relax and watch TV for the next 6-8 hours. Or if you want to sell it back to the grid, you would earn maybe one or two cents (figuring energy costs are about 10-20 cents per kilowatt-hour).

On the other hand, a mobile phone battery stores only about 3 -5 joules of energy. So if you pump this device for just one second you have produced more than enough to fully charge your phone!

So, very good for small devices such as phones, flashlights, ipods, maybe even laptops. But no good for the average household appliance like TV, heater, stereo, computer, refrigerator and so on.