A nine-volt battery, the most common of which (and the one referred to here unless otherwise stated) is designated a PP3 battery

Battery (electricity)

An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...

, is shaped as a rounded rectangular prism. 9-volt batteries are commonly used in pocket transistor radio

Transistor radio

A transistor radio is a small portable radio receiver using transistor-based circuitry. Following their development in 1954 they became the most popular electronic communication device in history, with billions manufactured during the 1960s and 1970s...

s, smoke detector

Smoke detector

A smoke detector is a device that detects smoke, typically as an indicator of fire. Commercial, industrial, and mass residential devices issue a signal to a fire alarm system, while household detectors, known as smoke alarms, generally issue a local audible and/or visual alarm from the detector...

s, carbon monoxide

Carbon monoxide

Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

 alarms, guitar effect units, and radio-controlled vehicle

Radio control

Radio control is the use of radio signals to remotely control a device. The term is used frequently to refer to the control of model vehicles from a hand-held radio transmitter...

 controllers

Control system

A control system is a device, or set of devices to manage, command, direct or regulate the behavior of other devices or system.There are two common classes of control systems, with many variations and combinations: logic or sequential controls, and feedback or linear controls...

. They are also used as backup power to keep the time in digital clock

Digital clock

A digital clock is a type of clock that displays the time digitally, i.e. in cyphers, as opposed to an analog clock, where the time is displayed by hands. Digital clocks are often associated with electronic drives, but the "digital" description refers only to the display, not to the drive mechanism...

s and alarm clock

Alarm clock

An alarm clock is a clock that is designed to make a loud sound at a specific time. The primary use of these clocks is to awaken people from their night's sleep or short naps; they are sometimes used for other reminders as well. To stop the sound, a button or handle on the clock is pressed; but...

s.

Nine-volt alkaline batteries are constructed of six individual 1.5V LR61 cells enclosed in a wrapper.
These cells are slightly smaller than standard LR8D425 AAAA cells

AAAA Battery

The AAAA battery is 42.5 mm long and 8.3 mm in diameter. The alkaline cell weighs around 6.5 g and producing 1.5 V. This battery is also classified as LR8D425 and 25A...

 and can be used in their place for some devices, even though they are 3.5 mm shorter.

As of 2007, 9-volt batteries accounted for 4% of alkaline primary battery sales in the US. In Switzerland as of 2008, 9-volt batteries totalled 2% of primary battery sales and 2% of secondary battery sales.

Connectors

The connector (snap) consists of two connectors: one smaller circular (male) and one larger, typically either hexagonal or octagonal (female). The connectors on the battery are the same as on the connector itself; the smaller one connects to the larger one and vice versa. The same connector is used on most other battery types in the Power Pack (PP) series.
The battery has both terminals

Battery terminals

Battery terminals are the electrical contacts used to connect a load and/or charger to a single cell or multiple-cell battery. These terminals have a wide variety of designs, sizes, and features that are often not well documented....

 on one end. Battery polarization is obvious since mechanical connection is only possible in one configuration.

A problem with this style of connector is that it is very easy to connect two batteries together in a short circuit

Short circuit

A short circuit in an electrical circuit that allows a current to travel along an unintended path, often where essentially no electrical impedance is encountered....

, which quickly discharges both batteries, generating heat and possibly a fire. The clips on the nine-volt battery can be used to connect several nine-volt batteries in series to create higher voltage.

History

The PP3 appeared when portable transistorized radio receivers became common, and is still called a "transistor" battery by some manufacturers. The Eveready

Energizer Holdings

Energizer Holdings is an American manufacturer of batteries and personal care products, headquartered in Town and Country, Missouri. Its most well known brands are Energizer and Eveready batteries, Schick, Wilkinson Sword and Edge shaving products, Playtex feminine hygiene and baby products, and...

 company claims that it introduced this battery type in 1956.
Early transistorized radios and other equipment needed a low voltage battery, but the lowest voltage commonly available, small battery at that time was a 22.5V battery made for vacuum tube/thermionic valve radios. The 22.5V voltage was at the upper limit of the transistor voltage ratings, and it was clear that what was needed was a battery of lower voltage and high enough capacity to run the transistor radios for a reasonable time.

Technical specifications

These batteries are commonly named 9-volt, and also colloquially named PP3, Radio battery, Square (sic) battery, and Japan "006P".

They all have a rectangular shape; the dimensions are height 48.5 mm, length 26.5 mm, width 17.5 mm. Both terminals are at the small end and their centres are 12.7 mm apart.

Inside an alkaline or carbon-zinc 9-volt battery there are six cells, either cylindrical alkaline

Alkaline battery

Alkaline batteries are a type of primary batteries dependent upon the reaction between zinc and manganese dioxide . A rechargeable alkaline battery allows reuse of specially designed cells....

 or flat carbon-zinc

Zinc-carbon battery

A zinc–carbon dry cell or battery is packaged in a zinc can that serves as both a container and negative terminal. It was developed from the wet Leclanché cell . The positive terminal is a carbon rod surrounded by a mixture of manganese dioxide and carbon powder. The electrolyte used is a paste of...

 type, connected in series. Some brands use welded tabs internally to attach to the cells, others press foil strips against the ends of the cells.

Rechargeable nickel–cadmium (NiCd) and Nickel-metal hydride (NiMH) batteries have between six and eight 1.2 volt cells. Lithium versions use three 3.2 V cells - there is a rechargeable lithium polymer version. There is also a low self-discharge NiMH version.

Formerly, mercury batteries

Mercury battery

A mercury battery is a non-rechargeable electrochemical battery, a primary cell. Due to the content of mercury, and the resulting environmental concerns, the sale of mercury batteries is banned in many countries. Both ANSI and IEC have withdrawn standards for mercury batteries...

 were made in this size. They had higher capacity than carbon-zinc types, a nominal voltage of 8.4 volts, and very stable voltage output. Once used in photographic and measuring instruments or long-life applications, they are now unavailable due to environmental restrictions.

name
! ANSI

American National Standards Institute

The American National Standards Institute is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organization also coordinates U.S. standards with international...

/NEDA

National Electronic Distributors Association

The National Electronic Distributors Association, or NEDA, is a trade association in the United States of manufacturers and distributors.The association cooperates in standardization of names for components, such as batteries. NEDA is often cited by American manufacturers, along with ANSI, for...

name
! Typical capacity
(mAh

MAH

The National Security Service was the governmental intelligence organization of Turkey between 1926 and 1965, when it was replaced by the National Intelligence Organization ....

)
! COLSPAN=3 |Nominal voltage
|- valign="top"
| ROWSPAN=3 |Primary (disposable)
| Alkaline

Alkaline battery

Alkaline batteries are a type of primary batteries dependent upon the reaction between zinc and manganese dioxide . A rechargeable alkaline battery allows reuse of specially designed cells....

| 6LR61
| 1604A
| 565
| ROWSPAN=2 COLSPAN=3 ALIGN=CENTER VALIGN=MIDDLE |9
|-
|Zinc–carbon
|6F22
|1604D
|400
|-
|Lithium

Lithium battery

Lithium batteries are disposable batteries that have lithium metal or lithium compounds as an anode. Depending on the design and chemical compounds used, lithium cells can produce voltages from 1.5 V to about 3.7 V, over twice the voltage of an ordinary zinc–carbon battery or alkaline battery...

|
|1604LC
|1200
| COLSPAN=2 |
|9.6
|- VALIGN=TOP
| ROWSPAN=4|Rechargeable
|NiCd
|6KR61
|11604
|120
|7.2
| COLSPAN=2 |8.4 (some)
|-
| ROWSPAN=2 |NiMH

NIMH

NIMH or NiMH may refer to:*Nickel-metal hydride battery, a type of rechargeable battery*National Institute of Mental Health, a part of the United States National Institutes of Health...

| ROWSPAN=2 |6HR61
| ROWSPAN=2 |7.2H5
| ROWSPAN=2 |175-300
| ROWSPAN=2 |7.2
| COLSPAN=2 ALIGN=CENTER|some:
|-
|8.4
|9.6
|-
|Lithium-ion polymer
|
|
|520
| COLSPAN=3 ALIGN=CENTER|9
|}
References: