The Suunto Replacement Battery Kit includes a CR2430 battery, an O-ring, and a new lid, and fits Suunto 3-series watches, including the Vector, X-Lander, Altimax, Advizor, and Yachtsman. When you change the battery, carefully follow the instructions in the manual. Never use an old lid or O-ring. Check that the O-ring is clean and correctly in place before closing the battery compartment. This will ensure that the device remains waterproof.