Automotive battery

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A typical 12 V, 40 Ah lead-acid car battery Photo-CarBattery.jpg
A typical 12 V, 40 Ah lead-acid car battery

An automotive battery or car battery is a rechargeable battery that is used to start a motor vehicle. Its main purpose is to provide an electric current to the electric-powered starting motor, which in turn starts the chemically-powered internal combustion engine that actually propels the vehicle. Once the engine is running, power for the car's electrical systems is still supplied by the battery, with the alternator charging the battery as demands increase or decrease.


Battery in modern cars

Gasoline and diesel engine

Typically, starting uses less than three percent of the battery capacity. For this reason, automotive batteries are designed to deliver maximum current for a short period of time. They are sometimes referred to as "SLI batteries" for this reason, for starting, lighting and ignition. SLI batteries are not designed for deep discharging, and a full discharge can reduce the battery's lifespan. [1]

As well as starting the engine, an SLI battery supplies the extra power necessary when the vehicle's electrical requirements exceed the supply from the charging system. It is also a stabilizer, evening out potentially damaging voltage spikes. [2] While the engine is running most of the power is provided by the alternator, which includes a voltage regulator to keep the output between 13.5 and 14.5 V. [3] Modern SLI batteries are lead-acid type, using six series-connected cells to provide a nominal 12-volt system (in most passenger vehicles and light trucks), or twelve cells for a 24-volt system in heavy trucks or earth-moving equipment, for example. [4]

Gas explosions can occur at the negative electrode where hydrogen gas can build up due to blocked battery vents or a poorly ventilated setting, combined with an ignition source. [5] Explosions during engine start-up are typically associated with corroded or dirty battery posts. [5] A 1993 study by the US National Highway Traffic Safety Administration said that 31% of vehicle battery explosion injuries occurred while charging the battery. [6] The next-most common scenarios were while working on cable connections, while jump-starting, typically by failing to connect to the dead battery before the charging source and failing to connect to the vehicle chassis rather than directly to the grounded battery post, and while checking fluid levels. [5] [6] Close to two-thirds of those injured suffered chemical burns, and nearly three-fourths suffered eye injuries, among other possible injuries. [6]

Electric and hybrid cars

Electric vehicles (EVs) are powered by a high-voltage electric vehicle battery, but they usually have an automotive battery as well, so that they can use standard automotive accessories which are designed to run on 12 V. They are often referred to as auxiliary batteries.

Unlike conventional, internal combustion engined vehicles, EVs don't charge the auxiliary battery with an alternator—instead, they use a DC-to-DC converter to step down the high voltage to the required float-charge voltage (typically around 14 V). [7]


Early cars did not have batteries, as their electrical systems were limited. A bell was used instead of an electric horn, headlights were gas-powered, and the engine was started with a crank. Car batteries became widely used around 1920 as cars became equipped with electric starter motors. The sealed battery, which did not require refilling, was invented in 1971. [8]

The first starting and charging systems were designed to be 6-volt and positive-ground systems, with the vehicle's chassis directly connected to the positive battery terminal. [9] Today, almost all road vehicles have a negative ground system. [10] The negative battery terminal is connected to the car's chassis.

The Hudson Motor Car Company was the first to use a standardized battery in 1918 when they started using Battery Council International batteries. BCI is the organization that sets the dimensional standards for batteries. [11]

Cars used 6 V electrical systems and batteries until the mid-1950s. The changeover from 6 to 12 V happened when bigger engines with higher compression ratios required more electrical power to start. [12] Smaller cars, which required less power to start stayed with 6 V longer, for example the Volkswagen Beetle in the mid-1960s and the Citroën 2CV in 1970.

In the 1990s a 42V electrical system standard was proposed. It was intended to allow more powerful electrically driven accessories, and lighter automobile wiring harnesses. The availability of higher-efficiency motors, new wiring techniques, and digital controls, and a focus on hybrid vehicle systems that use high-voltage starter/generators have largely eliminated the push for switching the main automotive voltages. [13]


An automobile battery is an example of a wet cell battery, with six cells. Each cell of a lead storage battery consists of alternate plates made of a lead alloy grid filled with sponge lead (cathode plates) or coated with lead dioxide (anode). [14] Each cell is filled with a sulfuric acid solution, which is the electrolyte. Initially, cells each had a filler cap, through which the electrolyte level could be viewed and which allowed water to be added to the cell. The filler cap had a small vent hole which allowed hydrogen gas generated during charging to escape from the cell.

The cells are connected by short heavy straps from the positive plates of one cell to the negative plates of the adjacent cell. A pair of heavy terminals, plated with lead to resist corrosion, are mounted at the top, sometimes the side, of the battery. Early auto batteries used hard rubber cases and wooden plate separators. Modern units use plastic cases and woven sheets to prevent the plates of a cell from touching and short-circuiting.

In the past, auto batteries required regular inspection and maintenance to replace water that was decomposed during the operation of the battery. "Low-maintenance" (sometimes called "zero-maintenance") batteries use a different alloy for the plate elements, reducing the amount of water decomposed on charging. A modern battery may not require additional water over its useful life; some types eliminate the individual filler caps for each cell. A weakness of these batteries is that they are very intolerant of deep discharge, such as when the car battery is completely drained by leaving the lights on. This coats the lead plate electrodes with lead sulfate deposits and can reduce the battery's lifespan by a third or more.

VRLA batteries, also known as absorbed glass mat (AGM) batteries are more tolerant of deep discharge but are more expensive. [15] VRLA batteries do not permit addition of water to the cell. The cells each have an automatic pressure release valve, to protect the case from rupture on severe overcharge or internal failure. A VRLA battery cannot spill its electrolyte which makes it particularly useful in vehicles such as motorcycles.

Batteries are typically made of six galvanic cells in a series circuits. Each cell provides 2.1 volts for a total of 12.6 volts at full charge. [16] During discharge, at the negative (lead) terminal a chemical reaction releases electrons to the external circuit, and at the positive (lead oxide) terminal another chemical reaction absorbs electrons from the external circuit. This drives the electrons through the external circuit wire (an electrical conductor) to produce an electric current (electricity). As the battery discharges, the acid of the electrolyte reacts with the materials of the plates, changing their surface to lead sulfate. When the battery is recharged, the chemical reaction is reversed: the lead sulfate reforms into lead dioxide. With the plates restored to their original condition, the process may be repeated.

Some vehicles use other starter batteries. For weight savings, the 2010 Porsche 911 GT3 RS has a lithium-ion battery as an option; [17] from 2018 onward, all Kia Niro conventional hybrids feature one as well. [18] Heavy vehicles may have two batteries in series for a 24 V system or may have series-parallel groups of batteries supplying 24 V. [19]


Physical format

Batteries are grouped by physical size, type and placement of the terminals, and mounting style. [15]

Amp hours (Ah)

Ampere hours (Ah or A·h) is a unit related to the energy storage capacity of the battery. This rating is required by law in Europe.

The ampere hour rating is generally defined as the product of (the current a battery can provide for 20 hours at a constant rate, at 80 degrees F (26.6 °C), while the voltage drops to a cut-off of 10.5 volts) times 20 hours. In theory, at 80 degrees F, a 100 Ah battery should be able to continuously provide 5 amps for 20 hours while maintaining a voltage of at least 10.5 volts. It is important to realize that the relationship between the Ah capacity and the discharge rate is not linear; as the discharge rate is increased, the capacity decreases. A battery with a 100Ah rating generally will not be able to maintain a voltage above 10.5 volts for 10 hours while being discharged at constant rate of 10 amps. Capacity also decreases with temperature.

Cranking amperages (CCA, CA, MCA, HCA)

Reserve capacity minutes (RCM or RC)

A battery's ability to sustain a minimum stated electrical load; it is defined as the time (in minutes) that a lead-acid battery at 80 °F (27 °C) will continuously deliver 25 amperes before its voltage drops below 10.5 volts.[ citation needed ]

Group size

Battery Council International (BCI) group size specifies a battery's physical dimensions, such as length, width, and height. These groups are determined by the organization. [23] [24]

Date codes

Use and maintenance

Excess heat is a main cause of battery failures, as when the electrolyte evaporates due to high temperatures, decreasing the effective surface area of the plates exposed to the electrolyte, and leading to sulfation. Grid corrosion rates increase with temperature. [25] [26] Also low temperatures can lead to battery failure. [27]

If the battery is discharged to the point where it can't start the engine, the engine can be jump started via an external source of power. Once running, the engine can recharge the battery, if the alternator and charging system are undamaged. [28]

Corrosion at the battery terminals can prevent a car from starting due to electrical resistance, which can be prevented by the proper application of dielectric grease. [29] [30]

Sulfation is when the electrodes become coated with a hard layer of lead sulfate, which weakens the battery. Sulfation can happen when battery is not fully charged and remains discharged. [31] Sulfated batteries should be charged slowly to prevent damage. [32]

SLI batteries (starting, lighting, and ignition) are not designed for deep discharge, and their life is reduced when subjected to this. [33]

Starting batteries have plates designed for increased surface area and thus high instant current capability, whereas marine (hybrid) and deep cycle types will have thicker plates and more room at the bottom of the plates for spent plate material to gather before shorting the cell.

Car batteries using lead-antimony plates require regular topping-up with pure water to replace water lost due to electrolysis and evaporation. By changing the alloying element to calcium, more recent designs have reduced the rate of water loss. Modern car batteries have reduced maintenance requirements, and may not provide caps for addition of water to the cells. Such batteries include extra electrolyte above the plates to allow for losses during the battery life.

Some battery manufacturers include a built-in hydrometer to show the state of charge of the battery.

A positive (red) jumper cable connected to battery post. An optional hydrometer window is visible by the single jumper clamp. The black negative jumper clamp is not shown. CrocodileClamponBattery.jpg
A positive (red) jumper cable connected to battery post. An optional hydrometer window is visible by the single jumper clamp. The black negative jumper clamp is not shown.

The primary wear-out mechanism is the shedding of active material from the battery plates, which accumulates at the bottom of the cells and which may eventually short-circuit the plates. This can be substantially reduced by enclosing one set of plates in plastic separator bags, made from a permeable material. This allows the electrolyte and ions to pass through but keeps the sludge build up from bridging the plates. The sludge largely consists of lead sulfate, which is produced at both electrodes.

Environmental impact

Battery recycling of automotive batteries reduces the need for resources required for the manufacture of new batteries, diverts toxic lead from landfills, and prevents the risk of improper disposal. Once a lead–acid battery ceases to hold a charge, it is deemed a used lead-acid battery (ULAB), which is classified as hazardous waste under the Basel Convention. The 12-volt car battery is the most recycled product in the world, according to the United States Environmental Protection Agency. In the U.S. alone, about 100 million auto batteries a year are replaced, and 99 percent of them are turned in for recycling. [34] However, the recycling may be done incorrectly in unregulated environments. As part of global waste trade, ULABs are shipped from industrialized countries to developing countries for disassembly and recuperation of the contents. About 97 percent of the lead can be recovered. Pure Earth estimates that over 12 million Third-World people are affected by lead contamination from ULAB processing. [35]

See also

Related Research Articles

<span class="mw-page-title-main">Electrochemical cell</span> Electro-chemical device

An electrochemical cell is a device capable of either generating electrical energy from chemical reactions or using electrical energy to cause chemical reactions. The electrochemical cells which generate an electric current are called voltaic or galvanic cells and those that generate chemical reactions, via electrolysis for example, are called electrolytic cells. A common example of a galvanic cell is a standard 1.5 volt cell meant for consumer use. A battery consists of one or more cells, connected in parallel, series or series-and-parallel pattern.

<span class="mw-page-title-main">Uninterruptible power supply</span> Electrical device that uses batteries to prevent any interruption of power flow

An uninterruptible power supply or uninterruptible power source (UPS) is an electrical apparatus that provides emergency power to a load when the input power source or mains power fails. A UPS differs from an auxiliary or emergency power system or standby generator in that it will provide near-instantaneous protection from input power interruptions, by supplying energy stored in batteries, supercapacitors, or flywheels. The on-battery run-time of most uninterruptible power sources is relatively short but sufficient to start a standby power source or properly shut down the protected equipment. It is a type of continual power system.

<span class="mw-page-title-main">Nickel–metal hydride battery</span> Type of rechargeable battery

A nickel metal hydride battery is a type of rechargeable battery. The chemical reaction at the positive electrode is similar to that of the nickel–cadmium cell (NiCd), with both using nickel oxide hydroxide (NiOOH). However, the negative electrodes use a hydrogen-absorbing alloy instead of cadmium. NiMH batteries can have two to three times the capacity of NiCd batteries of the same size, with significantly higher energy density, although much less than lithium-ion batteries.

<span class="mw-page-title-main">Nickel–cadmium battery</span> Type of rechargeable battery

The nickel–cadmium battery is a type of rechargeable battery using nickel oxide hydroxide and metallic cadmium as electrodes. The abbreviation Ni-Cd is derived from the chemical symbols of nickel (Ni) and cadmium (Cd): the abbreviation NiCad is a registered trademark of SAFT Corporation, although this brand name is commonly used to describe all Ni–Cd batteries.

<span class="mw-page-title-main">Rechargeable battery</span> Type of electrical battery

A rechargeable battery, storage battery, or secondary cell, is a type of electrical battery which can be charged, discharged into a load, and recharged many times, as opposed to a disposable or primary battery, which is supplied fully charged and discarded after use. It is composed of one or more electrochemical cells. The term "accumulator" is used as it accumulates and stores energy through a reversible electrochemical reaction. Rechargeable batteries are produced in many different shapes and sizes, ranging from button cells to megawatt systems connected to stabilize an electrical distribution network. Several different combinations of electrode materials and electrolytes are used, including lead–acid, zinc–air, nickel–cadmium (NiCd), nickel–metal hydride (NiMH), lithium-ion (Li-ion), lithium iron phosphate (LiFePO4), and lithium-ion polymer.

<span class="mw-page-title-main">Lead–acid battery</span> Rechargeable battery type often used in motor vehicles

The lead–acid battery is a type of rechargeable battery first invented in 1859 by French physicist Gaston Planté. It is the first type of rechargeable battery ever created. Compared to modern rechargeable batteries, lead–acid batteries have relatively low energy density. Despite this, their ability to supply high surge currents means that the cells have a relatively large power-to-weight ratio. These features, along with their low cost, make them attractive for use in motor vehicles to provide the high current required by starter motors. Lead-acid batteries suffer from relatively short cycle lifespan and overall lifespan.

<span class="mw-page-title-main">Jump start (vehicle)</span>

A jump start, also called a boost, is a procedure of starting a motor vehicle that has a discharged or depleted battery. A temporary connection is made to the battery of another vehicle, or to some other external power source. The external supply of electricity recharges the disabled vehicle's battery and provides some of the power needed to crank the engine. Once the vehicle has been started, its normal charging system will recharge, so the auxiliary source can be removed. If the vehicle charging system is functional, leaving the engine running will restore the charge of the battery, although it is usually recommended to drive the vehicle for a few minutes after starting to speed up the recharging process.

<span class="mw-page-title-main">Nickel–iron battery</span> Type of rechargeable battery

The nickel–iron battery is a rechargeable battery having nickel(III) oxide-hydroxide positive plates and iron negative plates, with an electrolyte of potassium hydroxide. The active materials are held in nickel-plated steel tubes or perforated pockets. It is a very robust battery which is tolerant of abuse, and can have very long life even if so treated. It is often used in backup situations where it can be continuously charged and can last for more than 20 years. Due to its low specific energy, poor charge retention, and high cost of manufacture, other types of rechargeable batteries have displaced the nickel–iron battery in most applications.

Peukert's law, presented by the German scientist Wilhelm Peukert in 1897, expresses approximately the change in capacity of rechargeable lead–acid batteries at different rates of discharge. As the rate of discharge increases, the battery's available capacity decreases, approximately according to Peukert's law.

<span class="mw-page-title-main">Battery charger</span> Device used to provide electricity

A battery charger, recharger, or simply charger, is a device that stores energy in a battery by running an electric current through it. The charging protocol depends on the size and type of the battery being charged. Some battery types have high tolerance for overcharging and can be recharged by connection to a constant voltage source or a constant current source, depending on battery type. Simple chargers of this type must be manually disconnected at the end of the charge cycle. Other battery types use a timer to cut off when charging should be complete. Other battery types cannot withstand over-charging, becoming damaged, over heating or even exploding. The charger may have temperature or voltage sensing circuits and a microprocessor controller to safely adjust the charging current and voltage, determine the state of charge, and cut off at the end of charge. Chargers may elevate the output voltage proportionally with current to compensate for impedance in the wires.

<span class="mw-page-title-main">VRLA battery</span> Type of lead–acid battery

A valve regulated lead–acid (VRLA) battery, commonly known as a sealed lead–acid (SLA) battery, is a type of lead–acid battery characterized by a limited amount of electrolyte absorbed in a plate separator or formed into a gel; proportioning of the negative and positive plates so that oxygen recombination is facilitated within the cell; and the presence of a relief valve that retains the battery contents independent of the position of the cells.

<span class="mw-page-title-main">History of the battery</span> History of electricity source

Batteries provided the primary source of electricity before the development of electric generators and electrical grids around the end of the 19th century. Successive improvements in battery technology facilitated major electrical advances, from early scientific studies to the rise of telegraphs and telephones, eventually leading to portable computers, mobile phones, electric cars, and many other electrical devices.

<span class="mw-page-title-main">Automobile auxiliary power outlet</span>

An automobile auxiliary power outlet in an automobile was initially designed to power an electrically heated cigarette lighter, but became a de facto standard DC connector to supply electrical power for portable accessories used in or near an automobile directly from the vehicle's electrical system. Such include mobile phone chargers, cooling fans, portable fridges, electric air pumps, and power inverters.

<span class="mw-page-title-main">Deep-cycle battery</span> Electrical storage system built for intensive discharging

A deep-cycle battery is a battery designed to be regularly deeply discharged using most of its capacity. The term is traditionally mainly used for lead–acid batteries in the same form factor as automotive batteries; and contrasted with starter or 'cranking' automotive batteries designed to deliver only a small part of their capacity in a short, high-current burst for cranking the engine.

UltraBattery is a hybrid energy storage device invented by Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO). UltraBattery combines ultracapacitor technology with lead-acid battery technology in a single cell with a common electrolyte.

<span class="mw-page-title-main">Electric battery</span> Power source with electrochemical cells

A battery is a source of electric power consisting of one or more electrochemical cells with external connections for powering electrical devices. When a battery is supplying power, its positive terminal is the cathode and its negative terminal is the anode. The terminal marked negative is the source of electrons that will flow through an external electric circuit to the positive terminal. When a battery is connected to an external electric load, a redox reaction converts high-energy reactants to lower-energy products, and the free-energy difference is delivered to the external circuit as electrical energy. Historically the term "battery" specifically referred to a device composed of multiple cells; however, the usage has evolved to include devices composed of a single cell.

In automobiles, a 42-volt electrical system was an electrical power standard proposed in the late 1990s. It was intended to allow more powerful electrically-driven accessories, and lighter automobile wiring harnesses. Electric motors were proposed to be used for power steering or other systems, providing more compact installations and eliminating the weight of drive belts or large wires for high-current loads. The proposed new standard was exactly triple the voltage of existing "12-volt" systems. The higher voltage was selected to provide greater power capacity for wiring and devices on one hand, and to stay under the 50-volt limit used as a guideline for electric shock hazard. The European auto manufacturer Daimler-Benz proposed a 42V brand name for the conversion.

<span class="mw-page-title-main">Battery regenerator</span>

A battery regenerator is a device that restores capacity to lead-acid batteries, extending their effective lifespan. They are also known as desulphators, reconditioners or pulse conditioning devices.

OPzS is used to refer to a flooded type of tubular-plated, lead acid deep cycle batteries. These batteries generally have a cell voltage of 2 volts and are connected in series to produce higher voltages. These types of batteries are generally vented and are used in stationary applications like solar, wind, and backup energy storage. They contain a liquid electrolyte which is generally composed of diluted sulfuric acid.

A silver–cadmium battery is a type of rechargeable battery using cadmium metal as its negative terminal, silver oxide as the positive terminal, and an alkaline water-based electrolyte. It produces about 1.1 volts per cell on discharge, and about 40 watthours per kilogram specific energy density. A silver–cadmium battery provides more energy than a nickel–cadmium cell of comparable weight. It has higher life cycle expectancy than silver–zinc cells, but lower terminal voltage and lower energy density. However, the high cost of silver and the toxicity of cadmium restrict its applications.


  1. Johnson, Larry. "Battery Tutorial". Charging Chargers. Retrieved 2016-02-15.
  2. "What is a lead battery?". Retrieved 2016-02-17.
  3. "Automotive Charging Systems – A Short Course on How They Work".
  4. "Q & A: Car Batteries". Retrieved 2016-02-18.
  5. 1 2 3 Vartabedian, Ralph (August 26, 1999), "How to Avoid Battery Explosions (Yes, They Really Happen)", Los Angeles Times
  6. 1 2 3 Injuries Associated With Hazards Involving Motor Vehicle Batteries, National Highway Traffic Safety Administration, July 1997
  7. Herron, David. "Why is there a 12 volt lead-acid battery, and how is it charged in an electric car?". Retrieved 24 May 2020.
  8. "History of the car battery". Archived from the original on 2016-12-28. Retrieved 2016-02-17.
  9. "Positive Vs. Negative Ground - Will charger work on positive ground vehicles?".
  10. "Why POSITIVE EARTH?". Retrieved 2019-04-20.
  11. "6-Volt Batteries". July 2006. Retrieved 2016-02-17.
  12. "6 Volt to 12 Volt Changeover". Retrieved 2016-02-17.
  13. "Whatever Happened to the 42-Volt Car?". Popular Mechanics. 2009-10-01. Retrieved 2016-02-18.
  14. Le, Thi Meagan (2001). Elert, Glenn (ed.). "Voltage of a car battery". The Physics Factbook. Retrieved 2022-01-24.
  15. 1 2 "How to Get the Right Car Battery". Consumer Reports. Retrieved 2016-02-17.
  16. "Basic Battery Care". Popular Mechanics. 2006-03-29. Retrieved 2016-02-17.
  17. Wert, Ray (2009-08-19). "2010 Porsche 911 GT3 RS: Track-Ready, Street-Legal And More Power". Archived from the original on 21 October 2009. Retrieved 2009-09-18.
  18. "2017 Kia Niro: The Troublemaker - The Car Guide". Retrieved 2022-03-09.
  19. "Automotive/SLI Batteries - Batteries by Fisher". Batteries by Fisher. Archived from the original on 2016-02-06. Retrieved 2016-02-15.
  20. 1 2 "From Our Experts: Car Battery Tips". Consumer Reports . December 2, 2015. Archived from the original on December 6, 2015. Retrieved 2016-02-17.
  21. "Winter Is Coming... Do You Know Your Battery's CCA Rating?". Bauer Built Inc. Archived from the original on 2019-03-02. Retrieved 2021-05-14.
  22. "Marine Battery vs. Car Battery: What Are the Differences?". October 4, 2018.
  23. "BCI Battery Service Manual 14th Edition - Download - Battery Council International". Archived from the original on 2020-08-07. Retrieved 2019-03-01.
  24. "bci-battery-technical-manual".
  25. Ruetschi, Paul (March 10, 2004), "Aging mechanisms and service life of lead–acid batteries", Journal of Power Sources , 127 (1–2): 33–44, Bibcode:2004JPS...127...33R, doi:10.1016/j.jpowsour.2003.09.052
  26. "Car batteries Buying Guide", Consumer Reports , August 2016
  27. The Most Common Reasons for 12 Volt Car Battery Drain
  28. Magliozzi, Tom; Magliozzi, Ray (April 1, 2007), "Is revving the engine a good idea during a jump-start? Find out", Car Talk , Tappet Brothers
  29. Meyer, Alex (17 December 2017). "Why do car batteries corrode?". Gear4Wheels.
  30. "How to Clean Corroded Car Battery Terminals". wikiHow.
  31. "Description and treatment of sulphated batteries using the mmf charger and the discharger/analyzer".
  32. Witte, O.A. (1922). The Automotive Storage Battery Its Care and Repair. The American Bureau of Engineering. (Full text via Project Gutenberg.)
  33. Johnson, Larry. "Battery Tutorial". Retrieved 2016-02-15.
  34. "Who Knew? A Car Battery Is the World's Most Recycled Product". Green Car Reports. Retrieved 2016-02-18.
  35. "Projects Reports". Retrieved 2016-02-18.