303/357 (SR44) Watch Batteries
The 303/357 battery is a silver oxide button cell used in many popular brand-name watches. You may also find it as a power source for hand-held calculators and other small devices. It is also known as an SR44 or K576 and is a direct replacement for LR44, AG13, SG13 and several other cells. This style is among the largest of the most common watch batteries with a case that measures 11.6mm in diameter by 5.4mm thick. The output is 1.55V and typical capacities are in the 170 - 200mAh range.
NOTE: There are a wide range of button cells with this diameter, in various thicknesses, so be certain to check the manufacturer’s replacement list when in doubt.