Shake Light or Fake Light?

The "shake light" AKA Faraday light, is a flashlight that is charged by kinetic energy. The user shakes the light front to back and this sends a magnet repeatedly through an induction coil which is supposed to generate enough electrical current to charge a capacitor. This charge is supposed to power the light for at least short time. There are fakes on the market. These look like shake lights, but are actually powered by small batteries. When the batteries die, the light will stop working.