Energizer Button Battery, 1.55V, 4.8mm Diameter

The Energizer Low drain watch battery uses a zinc/monovalent silver oxide chemical system and provides a nominal voltage of 1.55 volts with a capacity of 8 mAh, measured under a 56.2 kΩ discharge at 23±3°C down to 1.2 volts. It operates efficiently within a temperature range of 0°C to 60°C and features a low self-discharge rate of less than 7% per year at room temperature. Weighing approximately 0.13 grams, this battery offers reliable, long-lasting power ideal for precision timepieces.

According IEC 60086-3 standard
Equivalent mercury containing battery range
Long shelf life so they are always ready when you need them
They have been extensively tested so you will never be disappointed