I know many of you have played with them in the stores and say they stay bright forever. WRONG...... These flashlights which are sold as batteryless, actually contain 2 flat disk batteries. Thats why you never have to shake them when new.
I dismantled one, and found the batteries. I removed the batteries and they work without the batteries as long as they are shook almost constantly. They stay on for over an hour after being shook, but the light is so dim it's useless, and a match is brighter.
Once again we as consumers, are being deceived by the advertisers.