Rechargeable batteries: they have a lot of different sizes. The rechargeable battery is best used in regular use, and continuous use of time is not very long in the torch. They are the ideal choice because they can at any time on the charger to charge the flashlight for daily household. Usually AA type rechargeable batteries can be replaced by the model of alkaline batteries, but their battery life and brightness will be slightly weaker. The torch designed for charging batteries, light bulbs with their voltage of the battery is consistent (such as wolf eyes 3.4 volt incandescent bulbs), so do not worry about the wrong voltage. Alkaline battery: the most common type of battery in the market. Alkaline batteries are most suitable for use in most of the torch on the current relatively low demand in general, the expiration time they have more than 7 years. It uses alkaline batteries, their power will decay very quickly, leading to the shiny flashlight with the use of time decreased. They can be found almost anywhere, but their cold resistance is not very good. Lithium battery: as the name suggests, is the use of lithium metal as a raw material, they are suitable for high current situation, but also with respect to the alkaline battery has a better cold resistance. Because the relationship between the use of lithium, lithium batteries are very light, so some waterproof flashlight with lithium battery can even float on the water. The AA type lithium battery is the only energizer with other types of batteries have the same size. 123 a battery is widely used in the current incandescent light bulb type flashlight short life time. Their prices are also higher than alkaline batteries. The lens of the lens is used to prevent the light bulb from being hit, and some of the lenses have a shape and texture, which are used to correct the light beam reflected from the reflecting bowl. There are a lot of different kinds of materials in the market, the most of which are plastic. Some flashlight is used in Lexan, a transparent, not broken and thermal plastic. There are a variety of different kinds of glass, such as Pyrex glass. The glass lens will generally appear in the high power flashlight highlighted, because this kind of flashlight will generate a large amount of heat, a plastic lens is easy to aging in this case and deformation. Princeton Tec Impact is the use of single lens LED flashlight. The focusing lens can focus the light beam into a spot. Although it is not very bright, but it can make use of LED in the distance, do not want a lot of ordinary LED flashlight.