DURACELL LR44, A76, or AG13 button cells are the most common of button cell batteries. They are manufactured in large quantities, and are available from every battery company with a range of button batteries.
All LR44 cells have a standard voltage of 1.5V, and size of 11.6mm in diameter by 5.4mm in height. As an alkaline button cell, they are inexpensive to produce. This allows for really cheap prices to end users. The multitude of battery suppliers has resulted in many different names for the A76 battery, including LR44, AG13, G13, L1154, V13GA, plus many more.
LR44 button cells are used in hand-held electronic toys, calculators, LED lights in wheel nuts on cars, and just about every other place that a small amount of electricity is required at a low cost. In low-drain applications such as watches or calculators, an SG13 button cell (also called SR44, 357 or EPX76) can be used to replace the LR44. This uses Silver Oxide technology, and will last much longer. High power devices, such as laser pointers or toys are better off with an A76/LR44.