Includes 2 non-rechargeable (disposable) CR123 batteries Device works with containers with minimum 1.75 in. diameter opening (ie Nalgene wide-mouth bottles). SteriPen Portable UV Water Purifier System (ADO-RP): The Adventurer UV Pen is the smallest, lightest SteriPEN and uses a revolutionary optical eye to sense the water. The SteriPen ADO-RP destroys waterborne bacteria, viruses, and protozoa (giardia and cryptosporidium). Includes: 2 non-rechargeable (disposable) CR123 batteries and a neoprene case with belt loop. The Adventurer Steripen allows you to purify 8,000 doses of water. The Adventurer also works as a flashlight. The flashlight mode is activated by pressing and holding the single button down for 3 seconds. The Adventurer works with containers that are at least 1.75" in diameter (i.e. Nalgene wide mouth bottles.) WARNING: It is strongly recommended that you use a sediment filter like the FitsAll Filter below, before using a UV Light for purification