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Four double-A (AA)
In science and technology, a battery is a device that
energy and makes it available in an electrical form.
Batteries consist of
electrochemical devices such as two or more
fuel cells, or
The modern development of batteries started with the
Voltaic pile, announced by the Italian physicist
Alessandro Volta in 1800.
The worldwide battery industry generates
billion in sales annually
Formally, an electrical "battery" is an interconnected array
of similar voltaic cells ("cells"). However, in many
contexts it is common to call a single cell used on its own a
A Voltaic Pile, the first battery.
The earliest known artifacts that may have served as
batteries are the
Baghdad Batteries, which existed some time between
However, it is not known what electrical function they may have
served, and if they were in fact batteries at all. Scientists
have developed several theories about its use, including
medicine (as a
The story of the modern battery begins in
with the discovery of "animal electricity" by
Luigi Galvani. He created an
electric circuit consisting of two different metals, with
one touching the frog's leg and the other touching both the leg
and the first metal, thus closing the circuit. In modern terms,
the frog's leg served as both
detector, and the metals served as
electrodes. He noticed that even though the frog was dead,
its legs would twitch when he touched them with the metals.
Alessandro Volta realized that the frog could be replaced by
cardboard soaked in salt water, and another form of detection
could be employed. Having already studied the electrostatic
phenomenon of capacitance, Volta was able to quantitatively
measure the "voltage", or electromotive force (emf) associated
with each electrode-electrolyte interface, finding the emf to
always be on the order of a volt. Such a device is called a
voltaic cell, or cell for short. In 1799 Volta invented the
modern battery. He did this by placing many galvanic cells in
series, literally piling them one above the other. This
Voltaic Pile gave a greatly enhanced net emf for the
combination. (In many parts of Europe, batteries are called
piles.) Later researchers placed galvanic cells in parallel.
Such banks of cells are called batteries, presumably after the
earlier use by Benjamin Franklin to describe Leyden jars
(capacitors) in series and in parallel.
Although early batteries were of great value for experimental
purposes, their limitations made them impractical for large
current drain. Later batteries, starting with the
Daniell cell in 1836, provided more reliable currents and
were adopted by industry for use in stationary devices,
particularly in telegraph networks where, in the days before
electrical distribution networks, they were the only practical
source of electricity. These wet cells used liquid electrolytes,
which were prone to leaks and spillage if not handled correctly.
Some, like the
gravity cell, could only function in a certain orientation.
Many used glass jars to hold their components, which made them
fragile. These characteristics made wet cells unsuitable for
portable appliances. Near the end of the 19th century, the
invention of dry cell batteries, which replaced liquid
electrolyte with a paste made portable electrical devices
How batteries work
Circuit symbol for a battery; simplified electrical
model; and more complex but still incomplete model
(the series capacitor has an extremely large value
and, as it charges, simulates the discharge of the
A battery is a device in which chemical energy is directly
converted to electrical energy. It consists of one or more
voltaic cells, each of which is composed of two
half cells connected in series by the conductive
electrolyte. In the figure, the battery consists of one or more
voltaic cells in series. (The conventional symbol does not
necessarily represent the true number of voltaic cells.) Each
cell has a positive terminal, shown by a long horizontal line,
and a negative terminal, shown by the shorter horizontal line.
These do not touch each other but are immersed in a solid or
liquid electrolyte. In a practical cell the materials are
enclosed in a container, and a separator between the electrodes
prevents them from touching.
As discovered by Volta, each half cell can be assigned an
emf, with the net emf E being the difference between the emfs E1
and E2 of the half-cells; two identical half-cells annul one
another, giving zero net emf.
Unfortunately, Volta did not appreciate that the emf was due to
chemical reactions. He thought that his cells were an
inexhaustible source of energy, and that the associated chemical
effects (e.g., corrosion) were a mere nuisance -- rather than,
Michael Faraday showed around 1830, an unavoidable
by-product of their operation.
The electrolyte conducts current by allowing the passage of
between the two electrodes. Such reactions are called
faradaic, and are responsible for current flow through the
cell. Non-charge-transferring (non-faradaic) reactions
also occur at the electrode-electrolyte interfaces. Non-faradaic
reactions are one reason that voltaic cells (particularly the
lead-acid cell of ordinary batteries) "run down" when sitting
The electrical potential across the terminals of a battery is
known as its terminal voltage, measured in
The terminal voltage of a battery that is neither charging nor
open-circuit voltage) equals its
emf. The terminal voltage of a battery that is discharging
is less than the emf, and that of a battery that is charging is
greater than the emf.
The voltage produced by a cell depends on the chemicals used
in it, which have different electrochemical potentials. For
example, alkaline and carbon-zinc cells both have emfs of about
1.5 volts, due to the energy release of the associated chemical
reactions. Because of the high electrochemical potentials of
lithium compounds, Li cells can provide as much as 3 or more
Classification of batteries
Batteries are usually divided into two broad classes:
- Primary batteries irreversibly transform chemical
energy to electrical energy. Once the initial supply of
reactants is exhausted, energy cannot be readily restored to
the battery by electrical means.
- Secondary batteries can have the chemical
reactions reversed by supplying electrical energy to the
cell, restoring their original composition.
Historically, some types of primary batteries used, for
telegraph circuits, were restored to operation by replacing
the components of the battery consumed by the chemical reaction.
Secondary batteries are not indefinitely rechargeable due to
dissipation of the active materials, loss of electrolyte, and
Main battery features
discharge temperature range.
discharge C rate.
Cycle life (charge and discharge cycles).
Battery capacity and discharging
The more electrolyte and electrode material in the cell, the
greater the capacity of the cell. Thus a tiny cell has much less
capacity than a much larger cell, even if both rely on the same
chemical reactions (e.g.alkaline
cells), which produce the same terminal voltage.
Because of the chemical reactions within the cells, the
capacity of a battery depends on the
discharge conditions such as the magnitude of the current,
the duration of the current, the allowable terminal voltage of
the battery, temperature, and other factors.
The available capacity of a battery depends upon the rate at
which it is discharged. If a battery is discharged at a
relatively high rate, the available capacity will be lower than
expected. Therefore, a battery rated at 100 A·h will deliver 20
A over a 5 hour period, but if it is instead discharged at 50 A,
it will run out of charge before the theoretically expected 2
hours. For this reason, a battery capacity rating is always
related to an expected discharge duration, such as 15 minutes, 8
hours, 20 hours or others.
The relationship between current, discharge time, and
capacity for a lead acid battery is expressed by
Peukert's law. The
efficiency of a battery is different at different discharge
rates. When discharging at low rate, the battery's energy is
delivered more efficiently than at higher discharge rates.
Battery manufacturers use a standard method to rate their
batteries. The battery is discharged at a constant rate of
current over a fixed period of time, such as 10 hours or 20
hours, down to a set terminal voltage per cell. So a
100 ampere-hour battery is rated to provide 5 A for 20 hours at
In general, the higher the ampere-hour rating, the longer the
battery will last for a certain load. Installing batteries with
different A·h ratings will not affect the operation of a device
rated for a specific voltage.
Conversion to energy
The A·h rating of a battery is related to the amount of
energy it stores when fully charged. If two batteries have
the same nominal
voltage, then the one with the higher A·h rating stores more
energy. It would also typically take longer to recharge.
The energy E available from a battery is approximately
- Q is the charge, and
- V is the nominal voltage.
- number of joules = number of ampere-hours × number of
volts × 3600 seconds per hour, or
- number of watt-hours = number of ampere-hours × number
In the previous example of a 2.3 A.h, 3 V battery, the energy
is E = 2.3*3600*3 = 24,840 J.
This is only an approximation, because the voltage during
discharge is not constant.
Secondary batteries always yield less energy than was used to
charge them, since (among other reasons) the terminal voltage
during charging is higher than during discharging.
Even if never taken out of the original package, disposable
(or "primary") batteries can lose two to twenty-five percent of
their original charge every year. This is known as the "self
discharge" rate and is due to non-current-producing "side"
chemical reactions, which occur within the cell even if no load
is applied to it. The rate of the side reactions is reduced if
the batteries are stored at low temperature, although some
batteries can be damaged by freezing. High or low temperatures
will reduce battery performance.
Rechargeable batteries self-discharge more rapidly than
disposable alkaline batteries; up to three percent a day
(depending on temperature). Due to their poor shelf life, they
should not be stored and then relied upon to power flashlights
or radios in an emergency. For this reason, it is a good idea to
keep alkaline batteries on hand. Ni-Cd Batteries are almost
always "dead" when purchased, and must be charged before first
Most NiMH and NiCd batteries can be charged several hundred
times. Also, they both can be completely discharged and then
recharged without their capacity being damaged or shortened.
Automotive lead-acid rechargeable batteries have a much
harder life. Because of vibration, shock, heat, cold, and
sulfation of their lead plates, few automotive batteries last
beyond six years of regular use. Automotive starting batteries
have many thin plates to provide as many amps as possible in a
reasonably small package, and are only drained a small amount
before being immediately recharged. Care should be taken to
avoid deep discharging a starter battery, since each
charge and discharge cycle causes active material to be shed
from the plates. When holes form in the plates it results in
less surface area for the chemical reaction, which results in
less measured voltage. Leaving a lead-acid battery in a deeply
discharged state for any length of time allows the sulfate to
become more deeply adhered to the plate, making sulfate removal
during the charging process difficult. This can result in less
available plate surface and the resulting lower voltage,
shortening the battery's life. "Deep-Cycle" lead-acid batteries
such as those used in electric golf carts have much thicker
plates to aid their longevity. The main benefit of lead-acid is
its low cost, the main drawbacks are their large size and weight
per a given capacity and voltage. Lead-acid batteries should
never be discharged to below 20% of their full capacity as
internal resistance will cause heat and damage when attempting
to recharge them. Deep-cycle lead-acid systems often use a
low-charge warning light or a low-charge power cut-off switch to
prevent the type of damage that will shorten the battery's life.
Special "reserve" batteries intended for long storage in
emergency equipment or munitions keep the electrolyte of the
battery separate from the plates until the battery is activated,
allowing the cells to be filled with the electrolyte. Shelf
times for such batteries can be years or decades. However, their
construction is more expensive than more common forms.
Battery life can be extended by storing the batteries at a
low temperature, as in a
freezer, because the chemical reactions in the batteries are
slower. Such storage can extend the life of alkaline batteries
by an insignificant 5%; however, the life of rechargeable
batteries can be extended dramatically from a few days to
In order to reach their full power, batteries must be returned
to room temperature; therefore, alkaline battery manufacturers
Duracell do not recommend refrigerating or freezing
A battery explosion is caused by the misuse or malfunction of
a battery, such as attempting to recharge a primary battery, or
short circuiting a battery. With car batteries, explosions
are most likely to occur when a short circuit generates very
large currents. In addition, car batteries liberate
hydrogen when they are overcharged (because of
electrolysis of the water in the electrolyte). Normally the
amount of overcharging is very small, as is the amount of
explosive gas developed, and the gas dissipates quickly.
However, when "jumping" a car battery, the high current can
cause the rapid release of large volumes of hydrogen, which can
be ignited by a nearby spark (for example, when removing the
When a battery is recharged at an excessive rate, an
explosive gas mixture of hydrogen and oxygen may be produced
faster than it can escape from within the walls of the battery,
leading to pressure build-up and the possibility of the battery
case bursting. In extreme cases, the battery acid may spray
violently from the casing of the battery and cause injury.
Additionally, disposing of a battery in fire may cause an
explosion as steam builds up within the sealed case of the
Overcharging -- that is, attempting to charge a battery
electrical capacity -- can also lead to a battery explosion,
leakage, or irreversible damage to the battery. It may also
cause damage to the charger or device in which the overcharged
battery is later used.
Disposable and rechargeable batteries
Various batteries(clockwise from bottom left): two
9-volt, two "AA", one "D", a cordless phone battery,
a camcorder battery, a 2-meter handheld ham radio
battery, and a button battery, one "C" and two
"AAA", plus a U.S. quarter, for scale
From top to bottom:Two
button cells, a 9 volt
PP3 battery, a
AAA battery, a
AA battery, a
C battery, a
D battery, a large
From a user's viewpoint, at least, batteries can be generally
divided into two main types: non-rechargeable (disposable)
rechargeable. Each is in wide usage.
Disposable batteries, also called primary cells, are
intended to be used once and discarded. These are most commonly
used in portable devices with either low current drain, only
used intermittently, or used well away from an alternative power
source. Primary cells were also commonly used for alarm and
communication circuits where other electric power was only
intermittently available. Primary cells cannot be reliably
recharged, since the chemical reactions are not easily
reversible and active materials may not return to their original
forms. Battery manufacturers recommend against attempting to
recharge primary cells, although some electronics enthusiasts
claim it is possible to do so using a special type of charger.
By contrast, rechargeable batteries or secondary cells
can be re-charged by applying electrical current, which reverses
chemical reactions that occur in use. Devices to supply the
appropriate current are called chargers or rechargers.
The oldest form of rechargeable battery still in modern usage
is the "wet
lead-acid battery. This battery is notable in that it
contains a liquid in an unsealed container, requiring that the
battery be kept upright and the area be well-ventilated to
ensure safe dispersal of the
hydrogen gas which is vented by these batteries during
overcharging. The lead-acid battery is also very heavy for the
amount of electrical energy it can supply. Despite this, its low
manufacturing cost and its high surge current levels make its
use common where a large capacity (over approximately 10Ah) is
required or where the weight and ease of handling are not
A common form of lead-acid battery is the modern wet-cell
car battery. This can deliver about 10,000
of power for a short period, and has a peak current output that
varies from 450 to 1100
amperes. An improved type of lead-acid battery called a
gel battery (or "gel cell") has become popular in
automotive industry as a replacement for the lead-acid wet cell.
The gel battery contains a semi-solid electrolyte to prevent
spillage, electrolyte evaporation, and out-gassing, as well as
greatly improving its resistance to damage from vibration and
heat. Another type of battery, the
Absorbed Glass Mat (AGM) suspends the electrolyte in a
special fibreglass matting to achieve similar results. More
portable rechargeable batteries include several "dry cell"
types, which are sealed units and are therefore useful in
mobile phones and
laptops. Cells of this type (in order of increasing
power density and cost) include
nickel metal hydride (NiMH), and
lithium-ion (Li-Ion) cells.
Not designed to be rechargeable - sometimes called "primary
Zinc-carbon battery - mid cost - used in light drain
Zinc-chloride battery - similar to zinc carbon but
slightly longer life
Alkaline battery - alkaline/manganese "long life"
batteries widely used in both light drain and heavy drain
Silver-oxide battery - commonly used in hearing aids
Lithium battery - commonly used in digital cameras.
Sometimes used in watches and computer clocks. Very long
life (up to ten years in wristwatches) and capable of
delivering high currents but expensive
Mercury battery - formerly used in digital watches,
radio communications, and portable electronic instruments,
no longer manufactured due to toxicity
Zinc-air battery - commonly used in hearing aids
Thermal battery - high temperature reserve. Almost
exclusively military applications.
Water-activated battery - used for
radiosondes and emergency applications
- main article:
A rechargeable lithium polymer
mobile phone battery.
Also known as secondary batteries or accumulators.
Lead-acid battery - used in vehicles, alarm systems and
uninterruptible power supplies. The major advantage of
this chemistry is its low cost - a large lead-acid battery
(e.g. 70Ah) is relatively inexpensive compared to batteries
based on other chemistries. However, this historically
important battery type has a lower energy/mass than other
battery types now available (see below).
Absorbed glass mat
Lithium ion battery - used in laptops (notebook PCs),
modern camera phones, some rechargeable MP3 players and most
other portable rechargeable digital equipment. This
relatively modern battery type has a very high energy/mass
(i.e. a light battery will store a lot of energy) and shows
Lithium ion polymer battery - similar characteristics to
lithium-ion, but with slightly less energy/mass. This
battery type can be shaped according to need, as in
ultra-thin (1 mm thick) cells for
Nickel metal hydride battery
Nickel-cadmium battery - used in many domestic
applications but being superseded by Li-Ion and Ni-MH types.
This chemistry gives the longest cycle life (over 1500
cycles), but has low energy/mass compared to Li-Ion and
Ni-MH. Ni-Cd cells using older technology suffer from memory
effect; this has been reduced drastically in modern
Molten salt battery
Almost any liquid or moist object that has enough ions to be
electrically conductive can serve as the electrolyte for a cell.
As a novelty or science demonstration, it is possible to insert
two electrodes made of different metals into a
lemon, potato, glass of soft drink, etc. and generate small
amounts of electricity. As of 2005, "two-potato clocks" are
widely available in hobby and toy stores; they consist of a pair
of cells, each consisting of a potato (lemon, etc.) with two
electrodes inserted into it, wired in series to form a battery
with enough voltage to power a digital clock. Homemade cells of
this kind are of no real practical use, because they produce far
less current—and cost far more per unit of energy generated—than
commercial cells, due to the need for frequent replacement of
the fruit or vegetable. In addition, in the two-book series
"Sneaky Uses for Everyday Things", there are instructions to
make a battery from a nickel, a penny, and a piece of
paper towel dipped in
salt water. Each of these can make up to 0.3 volts and when
many of them are used, they can replace normal batteries for a
short amount of time.
Lead acid cells can easily be manufactured at home, but a
tedious charge/discharge cycle is needed to 'form' the plates.
This is a process whereby lead sulfate forms on the plates, and
during charge is converted to lead dioxide (positive plate) and
pure lead (negative plate). Repeating this process results in a
microscopically rough surface, with far greater surface area
being exposed. This increases the current the cell can deliver.
For an example, see
Traction batteries are high power batteries designed to
provide propulsion to move a vehicle, such as an
electric car or tow motor. A major design consideration is
power to weight ratio since the vehicle must carry the
battery. While conventional lead acid batteries with liquid
electrolyte have been used, gelled electrolyte and (AGM-type)
can also be used, especially in smaller sizes. The largest
installations of batteries for propulsion of vehicles are found
submarines, although the toxic gas produced by seawater
contact with acide electrolyte is a considerable hazard.
Battery types commercially used in electric vehicles include:
- flooded type with liquid electrolyte.
AGM-type (Absorbed Glass Mat)
Zebra Na/NiCl2 battery operating at 270 °C
requiring cooling in case of temperature excursions
NiZn battery (higher cell voltage 1.6 V and thus 25%
increased specific energy, very short lifespan)
Lithium-ion batteries are now pushing out NiMh-technology
battery electric vehicles and
Flow batteries are a special class of battery where
additional quantities of
electrolyte are stored outside the main power cell of the
battery, and circulated through it by pumps or by movement. Flow
batteries can have extremely large capacities and are used in
marine applications and are gaining popularity in
grid energy storage applications.
vanadium redox batteries are typical examples of
commercially-available flow batteries.
Since their development over 250 years ago, batteries have
remained among the most expensive energy sources, and their
manufacture consumes many valuable resources and often involves
hazardous chemicals. For this reason many areas now have battery
recycling services available to recover some of the more
toxic (and sometimes valuable) materials from used batteries.
Batteries may be harmful or fatal if
This changes with the nanotechnology batteries.
Cells in series or in parallel
The cells in a battery can be connected in parallel, series,
or in both. A parallel combination of cells has the same
voltage as a single cell, but can supply a higher
current (the sum of the currents from all the cells). A
series combination has the same current rating as a single cell
but its voltage is the sum of the voltages of all the cells.
Most practical electrochemical batteries, such as 9
flashlight (torch) batteries and 12 V
automobile (car) batteries, have several cells connected in
series inside the casing. Parallel arrangements suffer from the
problem that, if one cell discharges faster than its neighbour,
current will flow from the full cell to the empty cell, wasting
power and possibly causing overheating. Even worse, if one cell
becomes short-circuited due to an internal fault, its neighbour
will be forced to discharge its maximum current into the faulty
cell, leading to overheating and possibly explosion. Cells in
parallel are therefore usually fitted with an electronic circuit
to protect them against these problems. In both series and
parallel types, the energy stored in the battery is equal to the
sum of the energies stored in all the cells.
Effect of a battery's internal
A battery can be simply modelled as a perfect voltage source
(i.e. one with zero internal
resistance) in series with a
resistor. The voltage source depends mainly on the chemistry
of the battery, not on whether it is empty or full. When a
battery runs down, its internal
resistance increases. When the battery is connected to a
load (e.g. a
light bulb), which has its own resistance, the resulting
voltage across the load depends on the ratio of the battery's
internal resistance to the resistance of the load. When the
battery is fresh, its internal resistance is low, so the voltage
across the load is almost equal to that of the battery's
internal voltage source. As the battery runs down and its
internal resistance increases, the voltage drop across its
internal resistance increases, so the voltage at its terminals
decreases, and the battery's ability to deliver
power to the load decreases.
The formula for calculating the voltage Vt at the
terminals of a battery is:
is the open-circuit voltage of the battery
is the battery's internal resistance
- I is the current
flowing through the battery
This can be rearranged to calculate the internal resistance
given the other quantities:
Some common Battery-related terms:
Watt, unit of power. One Watt equals approximately
- W/kg, Watts per kilogram, unit of energy per mass.
- W/l, Watts per liter, unit power per volume.
Watt-hour, unit of energy, or work. 1 Watt expended
continuously for 1 hour equals 1 Watt-hour.
- W•h/kg, Watt-hours per kilogram, unit of energy per
- W•h/l, Watt-hours per litre, unit of energy density.
- W•h/lb, Watt-hours per pound, unit of energy per mass.
List of battery types
Solid Electrolyte Interface (high resistance
Spotlight on Photovoltaics & Fuel Cells. Accessed 14
Banks, Sir Joseph (1800), "On the Electricity excited by
the mere Contact of conducting Substances of different
Kinds. In a Letter from Mr. Alexandro Volta, F.R.S.,
Professor of Natural Philosophy at the University of
Pavia, to the Rt. Hon. Sir. Joseph Banks, Bart. K.B.
P.R.S. Read June 26, 1800." Philosophical
Transactions of the Royal Society of London, 1800,
The paper was submitted in April 1800 and read before
the Royal Society on June 26, 1800:
Matthews, Michael R.; Fabio Bevilacqua, Enrico Giannetto
(2001). "Science Education and Culture: The
Contribution of History and Philosophy of Science".
ISBN 0-7923-6972-6. ,
p. 261. Some sources identify the year of
invention as 1799; e.g. "The voltaic pile... was
constructed by Volta in 1799, and became known in
England in 1800,"
Beard, George Miller (1883). A Practical Treatise on
the Medical and Surgical Uses of Electricity Including
Localized and General Faradization, Localized and
Central Galvanization, Franklinization, Electrolysis and
Galvano-cautery. Wood. ,
p. 30 The publication in 1800 "caused a sensation"
Hankins, Thomas Leroy (1985). Science and the
Enlightenment. Cambridge University Press. ISBN. p.
"Battery" (def. 6), The Random House Dictionary of
the English Language, the Unabridged Edition (2nd
edition), 1996 ed.
World Mysteries - Strange Artifacts, Baghdad Battery.
Retrieved 16 March 2007.
Luigi Galvani - Corrosion Doctors. Accessed 16 March
*Donald G. Fink and H. Wayne Beaty, Standard Handbook
for Electrical Engineers, Eleventh Edition,McGraw-Hill,
New York, 1978,
ISBN 0-07020974-X, chapter 11, section "Batteries
and Fuel Cells"
Ask Yahoo: Does putting batteries in the freezer make
them last longer?. Retrieved 7 March 2007.
Duracell: Battery Care. Retrieved 7 March 2007.
Battery Xtender. Retrieved 7 March 2007.
- David Linden and Thomas B. Reddy ed., Handbook Of
Batteries. McGraw-Hill (2001).
ISBN 0-0713-5978-8. This is rather technical.
- Electricity, Magnetism, and Light, by Wayne M.
Saslow, Academic (2002).
ISBN 0-12-619455-6. pp.302-304 contrasts fast and slow
discharge (and charge). pp.304-315 discusses capacity,
resistance, battery life, and energy storage.