Terrible. Complicated, expensive, fragile, and with poor performance. Look at the size of the actual battery! Hint: in normal batteries, the entire battery is t

Terrible. Complicated, expensive, fragile, and with poor performance. Look at the size of the actual battery! Hint: in normal batteries, the entire battery is the battery. This is almost as bad as "solar powered batteries." A battery-charging "shake light" would be more practical, ergonomic, durable, and affordable. You could just buy one, and it would work with your existing batteries.