9V

9V typically denotes a nominal voltage of nine volts in electrical systems. In consumer electronics, the term most often refers to the rectangular 9-volt battery, commonly known as the PP3 battery. This form factor is widely used for portable devices and for backup power in certain home sensing and audio applications.

Construction and chemistry: A standard 9V battery contains six 1.5-volt cells connected in series inside a single case, producing about 9V when fresh. The outer shell provides two opposing terminals. Alkaline and zinc-carbon are common primary chemistries; mercury-containing types have largely disappeared due to environmental concerns. Lithium 9V cells exist for longer shelf life and higher energy density. Rechargeable formats are available, typically based on NiMH chemistry, but they often have a lower end voltage (around 8.4V) and may not be compatible with all devices.

Performance and usage: Capacity varies with chemistry and discharge rate. Alkaline 9V cells offer modest capacity and voltage sag under load, making them suitable for low-drain devices such as smoke detectors, desktop meters, and some guitar pedals. Rechargeable NiMH 9V cells provide more cycle life but deliver a lower nominal voltage; lithium 9V cells can deliver higher energy density and longer life in appropriate devices.

Availability and safety: 9V batteries are widely available in electronics and hardware stores. Recycling follows local guidelines; they should not be incinerated. When not in use, store devices with the battery connection protected to prevent short circuits, and dispose of spent cells responsibly.

See also: 9-volt battery, PP3 battery, NiMH, lithium 9V.