No need to insert dry cells 15-30 Seconds of Shaking will give up to 5 minutes of continuous bright light! As the magnet passes the metal coil,electricity is generated. The Forever Flashlight uses Faraday Principle of induction Because of this,guarantees no replacement parts will ever be necessary! 1.Save money!Never buy batteries! 2.Waterproof case even floats. 3.Light visible for up to a mile. 4.It’s Maintenance Free. The flashlight that never lets you down!At home,in the car,in your camper,boat,or storm emergency kit,Forever Flashlight is always ready-even if you haven’t used or checked it in years! Have them customized with your logo or message to make an excellent corporate gift.