The Adventurer Opti UV water purifier is essential gear for thousands of adventurers and features a patent-pending technology an optical eye senses water to ensure safe use and effective treatments. The revolutionary optical water sensor doubles as an integrated LED flashlight for added convenience on the trail or around the campsite hold down the activation button for three seconds to illuminate the darkness. Rugged design and construction trusted by thousands of endurance athletes. Adventurer Opti is powered by two CR123 batteries making it a lightweight water purification system and keeping it operating effectively in even cold environments. The long-lasting UV lamp provides purifies up to 8,000 liters! Works in containers with a minimum 1.75 inch diameter opening. Like Nalgene wide-mouth bottles one liter bottles. Contents SteriPEN Adventurer Opti Water Purifier, two disposable non-rechargeable CR123 batteries, neoprene case with belt loop, and user's guide. Weight 3.8 oz Dimensions 6.1 x 1.5 x 1 in Lamp Life 8,000 treatments Battery CR123 included with purchase or RCR123 Minimium Bottle Diameter 35mm 1.4 inches . Filter Compatability none