BATTERY BUTTONS: 1.5-Volt, 3-Volt | Perfect for scientific demonstration

BATTERY BUTTONS: 1.5V, 3V

• Alkaline button type batteries are commonly used in laser pointers and stopwatches.
• Lithium button type batteries are commonly used in most calculators, watches and some balances.

(Wikipedia excerpt: ..."A button cell, watch battery, or coin battery is a small battery made of a single electrochemical cell and shaped as a squat cylinder typically 5 to 25 mm (0.197 to 0.984 in) in diameter and 1 to 6 mm (0.039 to 0.236 in) high – resembling a button. Stainless steel usually forms the bottom body and positive terminal of the cell; insulated from it, the metallic top cap forms the negative terminal.
Button cell use in RTC modules as power source

Button cells are used to power small portable electronics devices such as wrist watches, pocket calculators, and remote key fobs. Wider variants are usually called coin cells. Devices using button cells are usually designed around a cell giving a long service life, typically well over a year in continuous use in a wristwatch. Most button cells have low self-discharge, holding their charge for a long time if not used. Relatively high-power devices such as hearing aids may use a zinc–air battery, which has a much higher capacity for a given size, but dries out after a few weeks even if not used..")