This sight is smaller than the former N-cell batter sight (511/551), and it is waterproof to 10 meters. It runs on a single CR123A battery, and it has a longer battery life than the N-cell style sights. With the single battery configuration, the XPS allows more rail space than ever, leaving more room for rear iron sights or NV mount. Smaller, lighter and always fast; the XPS series is a great addition. This Holographic Weapon Sight is night vision compatible with up to 10 settings for NV use.