Electric Optics Backpack Clasp Battery Pack is great for putting a couple feet of wire onto your book bag or backpack. This all in one Battery Pack, Inverter, and Heavy Duty Backpack Clasp is ideal making your backpack be seen at night. This small battery pack is great for many applications. It lights up 0-1.5 feet of EL Wire and is small enough to fit in the palm of your hand. It comes with a constant on/off switch and blink mode. Takes 3 (Three) L1145 Batteries (watch batteries).