AG0 L521 LR521 LR63 379
Size: 5.8 x 2.15 mm 1.5v Alkaline Manganese
Used in a wide variety of apllications including : Toys, Calculators, Watches, Clocks, Meters, LCD tools, Testers, Thermometers, and all manner of gadgets.
These can be used in place of Silver Oxide Cells in many applications as well, to save money, but bear in mind the voltage drop experienced, towards the end of the battery life, can mean more frequent replacements.
Generally sold in pairs or 10-packs, they are economical to purchase, compared to other types of watch battery.