E.g. This LED yoyo's battery nomenclature is: AG3 1 5VX2, meaning the yoyo uses 2 AG3 (LR41) batteries, each 1.5V, to power the LED lights.
AG3 1.5VX2 refers to batteries used in it:
AG3: A type of button cell battery (also called LR41).
1.5V: Voltage of one AG3 battery.
X2: 2 batteries are required.
AG3 (Alkaline) → LR41 (IEC standard)
SR41 (Silver Oxide version)
CR2032 (Lithium coin cell)