A pack of AAAA batteries.
The AAAA battery (usually read as quadruple-A) is 42.5 mm long and 8.3 mm in diameter. The alkaline cell weighs around 6.5 g and produces 1.5 V. This battery is also classified as LR8D425 (IEC)  and 25A (ANSI/NEDA). The battery is also known by its Duracell type number MN2500 or MX2500 and Energizer type number E96.
Collage of images showing the opening of a 9-volt battery to reveal six LR61 cells, which are similar to AAAA cells.
This battery size is most often used in small devices such as laser pointers, LED penlights, powered computer styluses, glucose meters and small headphone amplifiers. These batteries are not as popular as AAA or AA type batteries, and consequently are not as commonly available.
Some models of alkaline nine-volt battery may consist of a bundle of six LR61 cells inside, connected together by welded tabs. These cells are somewhat similar to AAAA cells and can be used in their stead in some devices, even though they are 3.5 millimetres (0.14 in) shorter. These cells are often unmarked so special care must be taken with polarity.
See also 
D, C, AA, AAA, AAAA
& 9-volt batteries
External links