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Rechargeable (or secondary) batteries contain active materials that can be regenerated by charging.

 

How Secondary Batteries Work

 

All batteries have positive and negative terminals, marked (+) and (-) respectively, and two corresponding electrodes.  The electrodes must not touch each other, and are separated by the electrolyte, which facilitates the flow of electric charge between the electrodes.  A collector conducts the charge to the battery's exterior and through the load.

 

When a battery is inserted into an electrical device, the device completes the circuit between the two terminals and triggers electrochemical reactions within the battery.  The anode undergoes an oxidation reaction with the electrolyte and releases electrons, while the cathode undergoes a reduction reaction and absorbs the free electrons.  The product of these two reactions is electricity, which is channeled out of the battery and into the device. 

 

When a secondary battery is recharged, its electrodes undergo an opposite process to the discharging action described above.  As the battery charger passes electricity through the battery, its cathode is oxidized and produces electrons which are then absorbed by the anode.  When the battery is fully charged, it can be connected to a load and discharged again.

 

Battery Chemistry

 

Manufacturers produce batteries using many different types of chemicals.  A battery's chemistry determines its size, voltage, and intended use.

  • Nickel cadmium (NiCd) batteries use nickel oxide hydroxide and cadmium as electrodes.  They are commonly available in consumer sizes as well as in battery packs.  NiCd batteries are manufactured for a wide range of applications, from toys and phones to electric vehicles and aircraft.

  • Silver oxide batteries use zinc and silver oxide as the negative and positive electrodes, respectively.  They have a very high energy-to-weight ratio but are expensive to produce due to the cost of silver.  They are typically manufactured as small cell batteries in order to limit the amount of silver used.

  • Nickel-metal hydride (NiMH) batteries are similar to the NiCd type and feature a metal alloy electrode in place of a cadmium one.  NiMH batteries are a relatively recent development, and can have two to three times the capacity of a NiCd battery.  A low self-discharge NiMH (LDS NiMH) battery, which features a longer shelf life, was introduced in 2005 by Sanyo.

  • Lithium titanium disulfide batteries use a titanium disulfide cathode.  They feature a high energy density and relatively flat discharge. 

  • Lithium polymer batteries are very similar to lithium ion types.  Lithium polymer batteries feature a polymer electrolyte solvent instead of the lithium ion battery's organic solvent.  The polymer solvent makes lithium polymer batteries more flexible, rugged, adaptable, and cheaper to produce.  They are commonly used in radio-controlled vehicles, portable consumer electronics, and electric vehicles.

  • Lithium ion batteries use a carbon anode, metal oxide cathode, and a lithium salt electrolyte solution.  They have excellent energy density and capacity.  Lithium ion batteries are very commonly used in portable consumer electronics, such as cell phones and laptops. 

The following table compares the most common types of secondary batteries. 

 

Chemistry

Voltage

Energy density

Power

Efficiency

(units)

Volts

Megajoules/kg

Watt hours/kg

Watts/kg

%

Nickel cadmium

1.2

0.14-0.22

30-40

150

70-90

Nickel-metal hydride

1.2

0.11-0.29

30-80

250-1000

66

Lithium ion

3.6

0.58

150-250

1800

99

Lithium polymer

3.7

0.47-0.72

130-200

3000

99.8

Silver oxide

1.86

 

130

 (high)

 

Table credit:  Electropaedia; Battery University

 

Battery Specifications

 

The GlobalSpec SpecSearch database contains information about a variety of standard sizes and shapes pertaining to both primary and secondary batteries.  These specifications can be classified by consumer sizes commonly available for general purpose applications, and non-consumer sizes for specialized uses such as photography and instrumentation.  Batteries manufactured for specialty use come in a variety of shapes and sizes.

 

When selecting industrial batteries, buyers should also specify the product's voltage, capacity and intended applications.

 

Consumer Sizes

  • Round batteries are taller than their diameter and have terminals on each end.  Depending on the active materials used, they typically produce between 1.2 and 3 volts when fresh.  Round batteries are commonly available in a variety of sizes, including AAA, AA, C and D.
  • 9-Volt or PP3 batteries consist of six individual 1.5 V cells within a can.  They are typically used in smoke detectors, alarms, and other consumer products. 

EIS

Consumer batteries.  Image credit:  EIS

Non-consumer Sizes

  • AAAA batteries are used in small devices such as laser pointers, penlights and glucose meters.
  • A batteries are approximately the same length as the AA size, but with a larger diameter.  They are commonly used in older laptop batteries and consumer battery packs. 
  • N batteries are roughly three-fifths the length of an AA battery.  Similarly to AAAA batteries, they are used in small device applications.
  • Sub-C batteries are typically used in consumer battery packs for power tools or radio-controlled vehicles.
  • Fractional batteries are expressed as a fractional number combined with a common battery size.  For example, a 1/2AA battery is half the length of an AA battery but shares the same diameter.  Common fractional batteries include 1/3AA, 2/3AA, 1/2A, 2/3A, 4/5sub-C and 1/2D.

Lead holder     Lead holder        Lead holder   Lead holder

Non-consumer batteries.  Left to right:  AAAA, N (with AA for scale), sub-C, 1/2AA (with AA).  Image credit:  Lead holder

Specialty Cells

  • Battery packs consist of primary or secondary batteries bundled together with a connector for use in phones, radio-controlled vehicles and other consumer devices. 
  • Coin or button cells are available in numerous sizes and are used in watches, calculators and hearing aids.
  • Lantern batteries typically produce 6 V and have spring or screw terminals.
  • Prismatic cells are rectangular batteries which have slightly lower energy densities than traditional cylindrical cells.  Although prismatic cells are expensive to manufacture, their unique construction offers a more efficient use of space, especially in designing battery packs.
  • Sachet cells are a relatively recent battery development designed to fit in a specific space.  Their electrodes are surrounded by a flexible foil packaging which replaces the hard case of traditional batteries, making sachet cells lighter.
  • Thin film batteries are very thin devices which can be integrated into circuits or plastic cards. 

 

Voltage

 

Battery voltage refers to the electric potential difference between the positive and negative terminal.  Manufacturers typically specify the battery's nominal voltage, although its actual discharge voltage can vary depending on the battery's charge and current.  For example, a battery cell with a nominal voltage of 2 V actually discharges between 1.7 and 2.0 V at a given time.  Most round consumer batteries carry a nominal voltage of 1.5 V, while a car battery is typically 12 volts.  Depending on the battery materials and application, voltage can range from a fraction of a volt to several kilovolts.

 

Capacity

 

The amount of charge a battery can store is known as its capacity.  Charge is typically measured in amp-hours or milliamp-hours (Ah or mAh).  Most manufacturers specify capacity as the constant current that a new battery can supply for 20 hours.  For example, a battery rated at 200 Ah can supply 10 A over a 20 hour period at room temperature.  If the current supply to the same battery is increased, the capacity will then decrease. 

 

Applications

 

Batteries are manufactured for use in numerous applications.

  • Consumer batteries are used for general purpose consumer applications, such as cameras, radio-controlled cars, toys, and laptops.
  • Energy batteries are manufactured for use in oil, natural gas and solar applications.
  • Industrial batteries are deep cycle batteries used in forklifts and other industrial applications.
  • Medical batteries are used for life support systems, hearing aids and wheelchairs.
  • Military batteries are often manufactured to MIL-SPEC requirements.
  • Transportation batteries are designed for use in aircraft, boats, automobiles and electric vehicles.

  • Stand-by/UPS batteries are used in uninterruptible power supplies (UPS) for emergency lighting and alarms.

References

 

Battery University - Learn about batteries

 

Scientific American - How do rechargeable batteries work?

Read user Insights about Rechargeable (Secondary) Batteries

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