What is All in One Battery and Why Do We Use Them?

Type of electrical battery

"Secondary battery" redirects here. For naval guns, see secondary armament

A battery bank used for an uninterruptible power supply in a data center A common consumer battery charger for rechargeable AA and AAA batteries

A rechargeable battery, storage battery, or secondary cell (formally a type of energy accumulator), 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 (Li-ion polymer).

Rechargeable batteries typically initially cost more than disposable batteries but have a much lower total cost of ownership and environmental impact, as they can be recharged inexpensively many times before they need replacing. Some rechargeable battery types are available in the same sizes and voltages as disposable types, and can be used interchangeably with them. Billions of dollars in research are being invested around the world for improving batteries as industry focuses on building better batteries.[1][2][3]

Applications

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Cylindrical cell (18650) prior to assembly. Several thousand of them (lithium ion) form the Tesla Model S battery (see Gigafactory). Lithium ion battery monitoring electronics (over- and discharge protection) Bloated lithium ion batteries, possibly damaged by faulty monitoring electronics

Devices which use rechargeable batteries include automobile starters, portable consumer devices, light vehicles (such as motorized wheelchairs, golf carts, electric bicycles, and electric forklifts), road vehicles (cars, vans, trucks, motorbikes), trains, small airplanes, tools, uninterruptible power supplies, and battery storage power stations. Emerging applications in hybrid internal combustion-battery and electric vehicles drive the technology to reduce cost, weight, and size, and increase lifetime.[4]

Older rechargeable batteries self-discharge relatively rapidly, and require charging before first use; some newer low self-discharge NiMH batteries hold their charge for many months, and are typically sold factory-charged to about 70% of their rated capacity.

Battery storage power stations use rechargeable batteries for load-leveling (storing electric energy at times of low demand for use during peak periods) and for renewable energy uses (such as storing power generated from photovoltaic arrays during the day to be used at night). Load-leveling reduces the maximum power which a plant must be able to generate, reducing capital cost and the need for peaking power plants.

According to a report from Research and Markets, the analysts forecast the global rechargeable battery market to grow at a CAGR of 8.32% during the period 2018–2022.[5]

Small rechargeable batteries can power portable electronic devices, power tools, appliances, and so on. Heavy-duty batteries power electric vehicles, ranging from scooters to locomotives and ships. They are used in distributed electricity generation and in stand-alone power systems.

Charging and discharging

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A solar-powered charger for rechargeable AA batteries

During charging, the positive active material is oxidized, producing electrons, and the negative material is reduced, consuming electrons. These electrons constitute the current flow in the external circuit. The electrolyte may serve as a simple buffer for internal ion flow between the electrodes, as in lithium-ion and nickel-cadmium cells, or it may be an active participant in the electrochemical reaction, as in lead–acid cells.

The energy used to charge rechargeable batteries usually comes from a battery charger using AC mains electricity, although some are equipped to use a vehicle's 12-volt DC power outlet. The voltage of the source must be higher than that of the battery to force current to flow into it, but not too much higher or the battery may be damaged.

Chargers take from a few minutes to several hours to charge a battery. Slow "dumb" chargers without voltage or temperature-sensing capabilities will charge at a low rate, typically taking 14 hours or more to reach a full charge. Rapid chargers can typically charge cells in two to five hours, depending on the model, with the fastest taking as little as fifteen minutes. Fast chargers must have multiple ways of detecting when a cell reaches full charge (change in terminal voltage, temperature, etc.) to stop charging before harmful overcharging or overheating occurs. The fastest chargers often incorporate cooling fans to keep the cells from overheating. Battery packs intended for rapid charging may include a temperature sensor that the charger uses to protect the pack; the sensor will have one or more additional electrical contacts.

Different battery chemistries require different charging schemes. For example, some battery types can be safely recharged from a constant voltage source. Other types need to be charged with a regulated current source that tapers as the battery reaches fully charged voltage. Charging a battery incorrectly can damage a battery; in extreme cases, batteries can overheat, catch fire, or explosively vent their contents.

Positive and negative electrode vs. anode and cathode for a secondary battery

Rate of discharge

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Battery charging and discharging rates are often discussed by referencing a "C" rate of current. The C rate is that which would theoretically fully charge or discharge the battery in one hour. For example, trickle charging might be performed at C/20 (or a "20-hour" rate), while typical charging and discharging may occur at C/2 (two hours for full capacity). The available capacity of electrochemical cells varies depending on the discharge rate. Some energy is lost in the internal resistance of cell components (plates, electrolyte, interconnections), and the rate of discharge is limited by the speed at which chemicals in the cell can move about. For lead-acid cells, the relationship between time and discharge rate is described by Peukert's law; a lead-acid cell that can no longer sustain a usable terminal voltage at a high current may still have usable capacity, if discharged at a much lower rate. Data sheets for rechargeable cells often list the discharge capacity on 8-hour or 20-hour or other stated time; cells for uninterruptible power supply systems may be rated at 15-minute discharge.

The terminal voltage of the battery is not constant during charging and discharging. Some types have relatively constant voltage during discharge over much of their capacity. Non-rechargeable alkaline and zinc–carbon cells output 1.5V when new, but this voltage drops with use. Most NiMH AA and AAA cells are rated at 1.2 V, but have a flatter discharge curve than alkalines and can usually be used in equipment designed to use alkaline batteries.

Battery manufacturers' technical notes often refer to voltage per cell (VPC) for the individual cells that make up the battery. For example, to charge a 12 V lead-acid battery (containing 6 cells of 2 V each) at 2.3 VPC requires a voltage of 13.8 V across the battery's terminals.

Damage from cell reversal

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Subjecting a discharged cell to a current in the direction which tends to discharge it further to the point the positive and negative terminals switch polarity causes a condition called cell reversal. Generally, pushing current through a discharged cell in this way causes undesirable and irreversible chemical reactions to occur, resulting in permanent damage to the cell. Cell reversal can occur under a number of circumstances, the two most common being:

• When a battery or cell is connected to a charging circuit the wrong way around.
• When a battery made of several cells connected in series is deeply discharged.

In the latter case, the problem occurs due to the different cells in a battery having slightly different capacities. When one cell reaches discharge level ahead of the rest, the remaining cells will force the current through the discharged cell.

Many battery-operated devices have a low-voltage cutoff that prevents deep discharges from occurring that might cause cell reversal. A smart battery has voltage monitoring circuitry built inside.

Cell reversal can occur to a weakly charged cell even before it is fully discharged. If the battery drain current is high enough, the cell's internal resistance can create a resistive voltage drop that is greater than the cell's forward emf. This results in the reversal of the cell's polarity while the current is flowing.[6][7] The higher the required discharge rate of a battery, the better matched the cells should be, both in the type of cell and state of charge, in order to reduce the chances of cell reversal.

In some situations, such as when correcting NiCd batteries that have been previously overcharged,[8] it may be desirable to fully discharge a battery. To avoid damage from the cell reversal effect, it is necessary to access each cell separately: each cell is individually discharged by connecting a load clip across the terminals of each cell, thereby avoiding cell reversal.

Damage during storage in fully discharged state

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If a multi-cell battery is fully discharged, it will often be damaged due to the cell reversal effect mentioned above. It is possible however to fully discharge a battery without causing cell reversal—either by discharging each cell separately, or by allowing each cell's internal leakage to dissipate its charge over time.

Even if a cell is brought to a fully discharged state without reversal, however, damage may occur over time simply due to remaining in the discharged state. An example of this is the sulfation that occurs in lead-acid batteries that are left sitting on a shelf for long periods. For this reason it is often recommended to charge a battery that is intended to remain in storage, and to maintain its charge level by periodically recharging it. Since damage may also occur if the battery is overcharged, the optimal level of charge during storage is typically around 30% to 70%.

Depth of discharge

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Depth of discharge (DOD) is normally stated as a percentage of the nominal ampere-hour capacity; 0% DOD means no discharge. As the usable capacity of a battery system depends on the rate of discharge and the allowable voltage at the end of discharge, the depth of discharge must be qualified to show the way it is to be measured. Due to variations during manufacture and aging, the DOD for complete discharge can change over time or number of charge cycles. Generally a rechargeable battery system will tolerate more charge/discharge cycles if the DOD is lower on each cycle.[9] Lithium batteries can discharge to about 80 to 90% of their nominal capacity. Lead-acid batteries can discharge to about 50–60%. While flow batteries can discharge 100%.[10]

Lifespan and cycle stability

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If batteries are used repeatedly even without mistreatment, they lose capacity as the number of charge cycles increases, until they are eventually considered to have reached the end of their useful life. Different battery systems have differing mechanisms for wearing out. For example, in lead-acid batteries, not all the active material is restored to the plates on each charge/discharge cycle; eventually enough material is lost that the battery capacity is reduced. In lithium-ion types, especially on deep discharge, some reactive lithium metal can be formed on charging, which is no longer available to participate in the next discharge cycle. Sealed batteries may lose moisture from their liquid electrolyte, especially if overcharged or operated at high temperature. This reduces the cycling life.

Recharging time

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BYD e6 taxi. Recharging in 15 Minutes to 80 percent

Recharging time is an important parameter to the user of a product powered by rechargeable batteries. Even if the charging power supply provides enough power to operate the device as well as recharge the battery, the device is attached to an external power supply during the charging time. For electric vehicles used industrially, charging during off-shifts may be acceptable. For highway electric vehicles, rapid charging is necessary for charging in a reasonable time.

A rechargeable battery cannot be recharged at an arbitrarily high rate. The internal resistance of the battery will produce heat, and excessive temperature rise will damage or destroy a battery. For some types, the maximum charging rate will be limited by the speed at which active material can diffuse through a liquid electrolyte. High charging rates may produce excess gas in a battery, or may result in damaging side reactions that permanently lower the battery capacity. Very roughly, and with many exceptions and caveats, restoring a battery's full capacity in one hour or less is considered fast charging. A battery charger system will include more complex control-circuit- and charging strategies for fast charging, than for a charger designed for slower recharging.

Active components

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The active components in a secondary cell are the chemicals that make up the positive and negative active materials, and the electrolyte. The positive and negative electrodes are made up of different materials, with the positive exhibiting a reduction potential and the negative having an oxidation potential. The sum of the potentials from these half-reactions is the standard cell potential or voltage.

In primary cells the positive and negative electrodes are known as the cathode and anode, respectively. Although this convention is sometimes carried through to rechargeable systems—especially with lithium-ion cells, because of their origins in primary lithium cells—this practice can lead to confusion. In rechargeable cells the positive electrode is the cathode on discharge and the anode on charge, and vice versa for the negative electrode.

Types

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Ragone plot of common types

Commercial types

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The lead–acid battery, invented in 1859 by French physicist Gaston Planté, is the oldest type of rechargeable battery. Despite having a very low energy-to-weight ratio and a low energy-to-volume ratio, its ability to supply high surge currents means that the cells have a relatively large power-to-weight ratio. These features, along with the low cost, makes it attractive for use in motor vehicles to provide the high current required by automobile starter motors.

The nickel–cadmium battery (NiCd) was invented by Waldemar Jungner of Sweden in 1899. It uses nickel oxide hydroxide and metallic cadmium as electrodes. Cadmium is a toxic element, and was banned for most uses by the European Union in 2004. Nickel–cadmium batteries have been almost completely superseded by nickel–metal hydride (NiMH) batteries.

The nickel–iron battery (NiFe) was also developed by Waldemar Jungner in 1899; and commercialized by Thomas Edison in 1901 in the United States for electric vehicles and railway signalling. It is composed of only non-toxic elements, unlike many kinds of batteries that contain toxic mercury, cadmium, or lead.

The nickel–metal hydride battery (NiMH) became available in 1989.[11] These are now a common consumer and industrial type. The battery has a hydrogen-absorbing alloy for the negative electrode instead of cadmium.

The lithium-ion battery was introduced in the market in 1991, is the choice in most consumer electronics, having the best energy density and a very slow loss of charge when not in use. It does have drawbacks too, particularly the risk of unexpected ignition from the heat generated by the battery.[12] Such incidents are rare and according to experts, they can be minimized "via appropriate design, installation, procedures and layers of safeguards" so the risk is acceptable.[13]

Lithium-ion polymer batteries (LiPo) are light in weight, offer slightly higher energy density than Li-ion at slightly higher cost, and can be made in any shape. They are available[14] but have not displaced Li-ion in the market.[15] A primary use is for LiPo batteries is in powering remote-controlled cars, boats and airplanes. LiPo packs are readily available on the consumer market, in various configurations, up to 44.4 V, for powering certain R/C vehicles and helicopters or drones.[16][17] Some test reports warn of the risk of fire when the batteries are not used in accordance with the instructions.[18] Independent reviews of the technology discuss the risk of fire and explosion from Lithium-ion batteries under certain conditions because they use liquid electrolytes.[19]

Other experimental types

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‡ citations are needed for these parameters

Notes

• a Nominal cell voltage in V.
• b Energy density = energy/weight or energy/size, given in three different units
• c Specific power = power/weight in W/kg
• e Energy/consumer price in W·h/US$ (approximately)
• f Self-discharge rate in %/month
• g Cycle durability in number of cycles
• h Time durability in years
• i VRLA or recombinant includes gel batteries and absorbed glass mats
• p Pilot production

Several types of lithium–sulfur battery have been developed, and numerous research groups and organizations have demonstrated that batteries based on lithium sulfur can achieve superior energy density to other lithium technologies.[37] Whereas lithium-ion batteries offer energy density in the range of 150–260 Wh/kg, batteries based on lithium-sulfur are expected to achieve 450–500 Wh/kg, and can eliminate cobalt, nickel and manganese from the production process.[22][38] Furthermore, while initially lithium-sulfur batteries suffered from stability problems, recent research has made advances in developing lithium-sulfur batteries that cycle as long as (or longer than) batteries based on conventional lithium-ion technologies.[39]

The thin-film battery (TFB) is a refinement of lithium ion technology by Excellatron.[40] The developers claim a large increase in recharge cycles to around 40,000 and higher charge and discharge rates, at least 5 C charge rate. Sustained 60 C discharge and 1000 C peak discharge rate and a significant increase in specific energy, and energy density.[41]

lithium iron phosphate batteries are used in some applications.

UltraBattery, a hybrid lead–acid battery and ultracapacitor invented by Australia's national science organisation CSIRO, exhibits tens of thousands of partial state of charge cycles and has outperformed traditional lead-acid, lithium, and NiMH-based cells when compared in testing in this mode against variability management power profiles.[42] UltraBattery has kW and MW-scale installations in place in Australia, Japan, and the U.S.A. It has also been subjected to extensive testing in hybrid electric vehicles and has been shown to last more than 100,000 vehicle miles in on-road commercial testing in a courier vehicle. The technology is claimed to have a lifetime of 7 to 10 times that of conventional lead-acid batteries in high rate partial state-of-charge use, with safety and environmental benefits claimed over competitors like lithium-ion. Its manufacturer suggests an almost 100% recycling rate is already in place for the product.

The potassium-ion battery delivers around a million cycles, due to the extraordinary electrochemical stability of potassium insertion/extraction materials such as Prussian blue.[43]

The sodium-ion battery is meant for stationary storage and competes with lead–acid batteries. It aims at a low total cost of ownership per kWh of storage. This is achieved by a long and stable lifetime. The effective number of cycles is above 5000 and the battery is not damaged by deep discharge. The energy density is rather low, somewhat lower than lead–acid.[citation needed]

Alternatives

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A rechargeable battery is only one of several types of rechargeable energy storage systems.[44] Several alternatives to rechargeable batteries exist or are under development. For uses such as portable radios, rechargeable batteries may be replaced by clockwork mechanisms which are wound up by hand, driving dynamos, although this system may be used to charge a battery rather than to operate the radio directly. Flashlights may be driven by a dynamo directly. For transportation, uninterruptible power supply systems and laboratories, flywheel energy storage systems store energy in a spinning rotor for conversion to electric power when needed; such systems may be used to provide large pulses of power that would otherwise be objectionable on a common electrical grid.

Ultracapacitors – capacitors of extremely high value – are also used; an electric screwdriver which charges in 90 seconds and will drive about half as many screws as a device using a rechargeable battery was introduced in 2007,[45] and similar flashlights have been produced. In keeping with the concept of ultracapacitors, betavoltaic batteries may be utilized as a method of providing a trickle-charge to a secondary battery, greatly extending the life and energy capacity of the battery system being employed; this type of arrangement is often referred to as a "hybrid betavoltaic power source" by those in the industry.[46]

Ultracapacitors are being developed for transportation, using a large capacitor to store energy instead of the rechargeable battery banks used in hybrid vehicles. One drawback of capacitors compared to batteries is that the terminal voltage drops rapidly; a capacitor that has 25% of its initial energy left in it will have one-half of its initial voltage. By contrast, battery systems tend to have a terminal voltage that does not decline rapidly until nearly exhausted. This terminal voltage drop complicates the design of power electronics for use with ultracapacitors. However, there are potential benefits in cycle efficiency, lifetime, and weight compared with rechargeable systems. China started using ultracapacitors on two commercial bus routes in 2006; one of them is route 11 in Shanghai.[47]

Flow batteries, used for specialized applications, are recharged by replacing the electrolyte liquid. A flow battery can be considered to be a type of rechargeable fuel cell.

Research

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Rechargeable battery research includes development of new electrochemical systems as well as improving the life span and capacity of current types.

See also

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References

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Further reading

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Components

Batteries are made up of three basic components: an anode, a cathode, and an electrolyte. A separator is often used to prevent the anode and cathode from touching, if the electrolyte is not sufficient. In order to store these components, batteries usually have some kind of casing.

OK, most batteries are not actually divided up in three equal sections, but you get the idea. A better cross-section of an alkaline cell can be found on Wikipedia

Both the anode and cathode are types of electrodes. Electrodes are conductors through which electricity enters or leaves a component in a circuit.

Anode

Electrons flow out from the anode in a device connected to a circuit. This means that conventional "current" flows into an anode.

On batteries, the anode is marked as the negative (-) terminal

In a battery, the chemical reaction between the anode and electrolyte causes a build up of electrons in the anode. These electrons want to move to the cathode, but cannot pass through the electrolyte or separator.

Cathode

Electrons flow into the cathode in a device connected to a circuit. This means that conventional "current" flows out from a cathode.

On batteries, the cathode is marked as the positive (+) terminal

In batteries, the chemical reaction in or around the cathode uses the electrons produced in the anode. The only way for the electrons to get to the cathode is through a circuit, external to the battery.

Electrolyte

The electrolyte is the substance, often a liquid or gel, that is capable of transporting ions between the chemical reactions that happen at the anode and cathode. The electrolyte also inhibits the flow of electrons between the anode and cathode so that the electrons more easily flow through the external circuit rather than through the electrolyte.

-> Alkaline batteries can leak their electrolyte, potassium hydroxide, if subjected to high heat or reverse voltage
(Image courtesy of Wiliam Davies of Wikimedia Commons) <-

The electrolyte is crucial in the operation of a battery. Because electrons cannot pass through it, they are forced to travel through electrical conductors in the form of a circuit that connect the anode to the cathode.

Separator

Separators are porous materials that prevent the anode and cathode from touching, which would cause a short circuit in the battery. Separators can be made from a variety of materials, including cotton, nylon, polyester, cardboard, and synthetic polymer films. Separators do not chemically react with either the anode, cathode, or electrolyte.

The voltaic pile used cloth or cardboard (separator) soaked in brine (electrolyte) to keep the electrodes apart

Ions in the electrolyte can be positively charged, negatively charged, and can come in a variety of sizes. Special separators can be manufactured that allow some ions to pass but not others.

Casing

Most batteries need a way to contain their chemical components. Casings, otherwise known as "housings" or "shells," are simply mechanical structures meant to hold the battery's internals.

This lead-acid battery has a plastic casing

Battery casings can be made of almost anything: plastic, steel, soft polymer laminate pouches, and so on. Some batteries use a conducting steel casing that is electrically connected to one of the electrodes. In the case of the common AA alkaline cell, the steel casing is connected to the cathode.

Operation

Batteries generally require several chemical reactions in order to operate. At least one reaction occurs in or around the anode and one or more reactions occur in or around the cathode. In all cases, the reaction at the anode produces extra electrons in a process called oxidation, and the reaction at the cathode uses the extra electrons during a process known as reduction.

When the switch is closed, the circuit is complete, and electrons can flow from the anode to the cathode. These electrons enable the chemical reations at the anode and cathode.

In essence, we are separating a certain kind of chemical reaction, a reduction-oxidation reaction or redox reaction, into two separate parts. Redox reactions occur when electrons are transferred between chemicals. We can harness the movement of electrons in this reaction to flow outside the battery to power our circuit.

Anode Oxidation

This first part of the redox reaction, oxidation, occurs between the anode and electrolyte, and it produces electrons (marked as e-).

Some oxidation reactions produce ions, such as in a lithium-ion battery. In other chemistries, the reaction consumes ions, like in the common alkaline battery. In either case, ions are able to flow freely through the electrolyte where electrons cannot.

Cathode Reduction

The other half of the redox reaction, reduction, occurs in or near the cathode. Electrons produced by the oxidation reaction are consumed during reduction.

In some cases, like lithium-ion batteries, positively charged lithium ions produced during the oxidation reaction are consumed during reduction. In other cases, like alkaline batteries, negatively charged ions are produced during reduction.

Electron Flow

In most batteries, some or all of the chemical reactions can occur even when the battery is not connected to a circuit. These reactions can impact a battery's shelf life.

For the most part, the reactions will only occur at full force when an electrically conductive circuit is completed between the anode and cathode. The less resistance between the anode and cathode, the more electrons are allowed to flow, and the quicker the chemical reactions occur.

Creating a short circuit in a battery (even accidental ones, in this case), can be dangerous. Lithium-ion batteries are known to overheat and even smoke or catch fire in the presence of a short circuit.

We can pass these moving electrons through various electrical components, known as a "load," in order to accomplish something useful. In the motion graphic at the beginning of this section, we are lighting a virtual light bulb with our moving electrons.

Dead Battery

The chemicals in the battery will ultimately reach a state of equilibrium. In this state, the chemicals will no longer have a tendency to react, and as a result, the battery will not generate any more electric current. At this point, the battery is considered "dead."

Primary cells must be disposed when the battery is dead. Secondary cells can be recharged, and this is accomplished by applying a reverse electric current through the battery. Recharging occurs when the chemicals perform another series of reactions to take them back to their original state.

Terminology

People often use a common set of terms when talking about a battery's voltage, capacity, current sourcing capability and so on.

Cell

A cell refers to a single anode and cathode separated by electrolyte used to produce a voltage and current. A battery can be made up of one or more cells. A single AA battery, for example, is one cell. Car batteries contain six cells at 2.1 V each.

The common 9-volt battery contains six 1.5 V alkaline cells stacked on top of each other

Primary

Primary cells contain chemistry that cannot be reversed. As a result, the battery must be thrown away after it is dead.

Secondary

Secondary cells can be recharged and have their chemistry reverted back to their original state. Otherwise known as "rechargeable batteries," these cells can be used many times.

Nominal Voltage

The nominal voltage of a battery is the voltage stated by the manufacturer.

For example, alkaline AA batteries are listed as having 1.5 V. This article from Mad Scientist Hut shows their tested alkaline batteries start at about 1.55 V and then slowly lose voltage as they are discharged. In this example, "1.5 V" nominal voltage refers to the maximum or starting voltage of the battery.

This Storm battery pack for quadcopters shows the discharge curve for their LiPo cells starting at around 4.2 V and dropping to around 2.8 V as it discharges. The nominal voltage listed for most lithium-ion and LiPo cells is 3.7 V. In this case, "3.7 V" nominal voltage refers to the average voltage of the battery over its discharge cycle.

Capacity

A battery's capacity is a measure of the amount of electric charge it can deliver at a specific voltage. Most batteries are rated in amp hours (Ah) or milliamp hours (mAh).

This LiPo battery is rated for 1000 mAh, which means it can provide 1 amp for 1 hour before it is considered dead.

Most battery discharge graphs show the battery's voltage as a function of capacity, such as these AA battery tests by PowerStream. To figure out if a battery has enough capacity to power your circuit, find the lowest acceptable voltage and find the associated mAh or Ah rating.

C-Rate

Many batteries, especially powerful lithium-ion batteries, express discharge current as "C-Rate" in order to more clearly define battery attributes. C-Rate is the rate of discharge relative to the battery's maximum capacity.

1C is the amount of current required to discharge the battery in 1 hour. For example, a 400 mAh battery supplying 1C of current would be supplying 400 mA. 5C for the same battery would be 2 A.

Most batteries lose capacity at higher current draws. For example, this product info graph from Chargery shows that their LiPo cell has less mAh at higher C-Rates.

NOTE: General advice holds that you should charge LiPo batteries at 1C or less.

MIT has a fantastic guide to battery specifications and terminology that goes much further that this overview.

Usage

Single Cell

Some circuits can be powered by a single cell, but make sure that the battery can provide enough voltage and current.

This Photon Battery Shield is being powered from a single LiPo cell

If the voltage is too high or too low for your circuit, you will likely need a DC/DC converter.

Series

In order to increase the voltage between a battery's terminals, you can place the cells in series. Series means stacking the cells end-to-end, connecting the anode of one to the cathode of the next.

By connecting batteries in series, you increase the total voltage. Add the voltage of all the cells to determine the operating voltage. The capacity stays the same.

In this example, four 1.5 V cells are connected in series. The voltage across the load is 6 V while the total set of batteries have a 2000 mAh capacity.

In most consumer electronics that use alkaline batteries, the batteries are stacked in series. For example, this 2x AA battery holder can raise the nominal voltage to 3 V for a project.

NOTE: If you are charging lithium-ion or LiPo batteries in series, you need to make sure to use special circuitry known as a "balancer" to ensure the voltages among the cells stays even. Some chargers, like

If you are charging lithium-ion or LiPo batteries in series, you need to make sure to use special circuitry known as a "balancer" to ensure the voltages among the cells stays even. Some chargers, like this one , have balancers to allow for safe charging.

Parallel

If the voltage of a single cell is adequate for the load, you can add batteries in parallel to increase the capacity. Note that this also means increasing the available current (C-Rate).

Be careful when connecting batteries in parallel! All the cells should have the same nominal voltage and same charge level. If there are any voltage differences, a short circuit could occur causing overheating and possibly fire.

In this example, four 1.5 V cells are connected in parallel. The voltage across the load stays at 1.5 V, but the total capacity increases to 8000 mAh.

Series and Parallel

If you want to increase voltage and capacity, you can combine series and parallel batteries. Once again, make sure that the voltage level is the same for the batteries in parallel, as a short circuit can occur.

In this example, the total voltage across the load is 3V, and the batteries' combined capacity is 4000 mAh.

In large battery packs, especially lithium-ion, you often see the configuration listed using 'S' and 'P' for series and parallel. The configuration for the circuit above is 2S2P. As a practical example, modern electric cars use massive arrays of batteries connected in series and parallel.