An AAAA battery is a small cylindrical battery that measures 8.3 mm in diameter and 42.5 mm in length. It is similar in shape to an AAA battery, but smaller in size. AAAA batteries are commonly used in small electronic devices such as penlights, laser pointers, and digital calipers. They have a nominal voltage of 1.5 volts and are usually made of Alkaline chemistry.