When a watch stops keeping time, the battery is often the first thing to check. If the existing cell is marked 321, replacing it with the correct specification can get the watch running again without unnecessary guesswork. For shoppers planning to Buy Watch Batteries 321 Online, the main challenge isn\'t finding a listing. There are plenty of them. The real challenge is making sure the battery you\'re ordering matches the watch, comes from a dependable battery supplier, and is stored and handled properly. The 321 watch battery is also commonly identified as SR616SW. It is a silver oxide cell with a nominal voltage of 1.55V. Its listed dimensions are approximately 6.8 mm in diameter and 1.6 mm in height. That gives buyers a useful starting point. But before placing an order, there are a few dos and don\'ts worth knowing.