I've had a Photon II on my keychain for almost three years now with the original 2 X CR2016 batteries. I love its size, weight, and reliability. I don't use it very often but when I do it comes in very handy. Its diminutive size allows me also carry a pill container, Spyderco LadyBug pocket knife, and measuring tape on my key chain as well. I don't need a bigger key chain light because I normally carry a Thorfire TGo6S in a belt pouch. Also on my belt, I normally carry a one of several types of Kershaw folding knives in a horizontal carry pouch.