KREINDO An Illustrated Field Guide Vol. I  ·  MMXXVI

An illustrated history & anatomy

On Batteries

From the first pile to the phone in your pocket

What’s inside one, how it works, who invented it, and how to get rid of it safely. Every fact is footnoted to its source.

In 1800 Alessandro Volta stacked discs of metal and brine-soaked cloth into a column and got something no one had had before: a steady electric current.13 Two centuries later, descendants of that pile start our cars, run our phones and power our clocks. This guide explains how they work, from the zinc and manganese in an AA to the lithium in a laptop, and lists where every fact comes from.

Begin at Chapter I ↓

Fig. 1Volta’s own plate, Philosophical Transactions, 1800: the “crown of cups” at the top and three arrangements of his pile below.2
1800

Alessandro Volta describes the first battery, a “pile” of zinc and copper discs, in a letter to the Royal Society.213

1.5 V

The nominal voltage of an ordinary alkaline AA cell, known to the standards bodies as IEC LR6.28

1991

The first lithium-ion batteries go on sale, and phones and laptops begin to shrink.1117

2019

Goodenough, Whittingham and Yoshino share the Nobel Prize in Chemistry for the lithium-ion battery.12

CHAPTER I

The Idea

Two materials, one barrier, and the long way round

A battery is chemistry kept waiting. Inside, two different materials want to trade electrons. A third material between them, the electrolyte, lets charged atoms (ions) through but blocks the electrons themselves. So the electrons take the long way round: out of one terminal, through your flashlight or phone, and back in at the other. That detour is the electric current.19

The electrode that gives up electrons is the anode. The one that takes them in is the cathode. Between them sits the electrolyte, usually with a porous separator that keeps the two from touching.19 When the anode runs out of electrons to give, the battery is flat. In a rechargeable battery, a charger pushes the electrons back where they started.

Strictly speaking, one of these units is a cell, and a battery is several cells wired together. Benjamin Franklin borrowed the word from the artillery, where a “battery” is a row of cannon firing together. He used it for a bank of linked Leyden jars in a letter to Peter Collinson. The letter is dated 1748 at the top and 29 April 1749 at the end, so sources give both years.2021 Franklin’s jars stored static charge rather than making it chemically. The first true chemical battery came half a century later.

The names of the parts came later still. In 1834 Michael Faraday published the words electrode, anode, cathode, electrolyte and ion in his Experimental Researches in Electricity,3 and some of the Greek roots were suggested by the polymath William Whewell.22

Anode Gk. anodos, “way up”
The electrode where oxidation happens. In a battery that is being used, it is the negative terminal and gives up electrons.319
Cathode Gk. kathodos, “way down”
The electrode where reduction happens. In a battery that is being used, it is the positive terminal and takes electrons in.319
Electrolyte
The material between the electrodes. It carries ions from one side to the other but blocks electrons.19
Separator
A thin porous layer that keeps the electrodes from touching while still letting ions through.19
Ion Gk. “going”
An atom or molecule carrying an electric charge. Ions are what actually move through the electrolyte.3
Cell & battery
A cell is one anode–electrolyte–cathode unit. A battery is several of them. A 9-volt alkaline is usually six 1.5-volt cells in one case.25
A cell at work An electrochemical cell: an anode and a cathode stand in an electrolyte, split by a separator. Electrons flow from the anode through a wire and a lamp to the cathode, while ions move through the electrolyte. electrons out electrons in + − ions drift through the electrolyte Anode (−) Cathode (+) Separator lamp
Fig. 2A cell at work. Electrons leave the anode through the wire and light the lamp. Inside, positive ions drift toward the cathode and negative ions toward the anode, so the charges stay balanced.19
CHAPTER II · PLATE I

Anatomy of an AA

The ordinary alkaline cell, taken apart

Plate IParts of a typical alkaline battery (AA). Click to enlarge.

The cylindrical alkaline cell, the AA in your television remote, went on sale in 1959 and still dominates the market for throwaway batteries.27

Its basic recipe comes from a patent filed on 9 October 1957 by Paul Marsal, Karl Kordesch and Lewis Urry of Union Carbide.7 Their key change was powdered zinc. A powder has far more surface area than a solid zinc can, so the cell can deliver much more current.18 Energizer’s engineering handbook still describes every part, and the list on the right follows it.27

Editor’s note Plate I shows the brass rod sending current to the positive terminal. In a real alkaline cell, the brass pin sits in the zinc anode and collects current for the negative end. The steel can collects it for the positive end.27
  • Steel canHolds the active materials and collects current from the cathode.27
  • CathodeHigh-purity manganese dioxide mixed with carbon to help it conduct.27
  • SeparatorSpecially chosen materials that stop solid particles from drifting between the electrodes.27
  • AnodeA gel of zinc powder mixed with the potassium hydroxide electrolyte.27
  • Brass collectorCollects current from the zinc anode.27
  • CoversThe positive and negative contacts, made of nickel-plated steel.27
  • LabelA non-conductive plastic film that insulates the cell.27
  • Nylon sealCloses the cell and acts as a safety vent.27
The reaction
Zn + 2MnO2 + H2O ⟶ ZnO + 2MnOOH

Zinc is oxidised at the anode and manganese dioxide is reduced at the cathode. Water is used up along the way. Never try to recharge one: when an alkaline cell is charged or shorted, it can give off large amounts of hydrogen gas.27

CHAPTER III

The Rocking-Chair Cell

How a lithium-ion battery charges and discharges

Most batteries work by slowly eating their own electrodes. The lithium-ion cell doesn’t. Its lithium ions slip in and out of layered materials, a process called intercalation, and the electrodes are left largely intact. The Nobel committee called this its greatest advantage.11

In a typical cell the anode is graphite and the cathode is an oxide of metals such as nickel, manganese and cobalt. A separator sits between them, and each side has a current collector that leads to the outside.19

  1. Discharging. Lithium ions leave the graphite, cross the electrolyte and settle into the cathode.1119
  2. The detour. The separator blocks electrons, so they go round through the external circuit, which is the part that powers your phone.19
  3. Charging. A charger drives electrons back into the anode, and the ions follow them home.1119
  4. Again. Because nothing is used up, the ions can rock back and forth through cycle after cycle. That is where the cell gets its nickname.
Lithium-ion cell, interactive Lithium ions move from the graphite anode to the metal-oxide cathode while the cell discharges, and back again while it charges. Electrons travel through the outer circuit.
Charged 100%
Fig. 3Press Discharge to light the lamp, or Charge to plug it in. You can also drag the slider. Each circle is a lithium ion. The dots on the wire are electrons.
CHAPTER IV · PLATE II

Two Centuries of Cells

The inventors, the dates and the documents

Swipe sideways to read the whole plate, or tap it to enlarge.

Plate IIA timeline of the invention of batteries. The full chronology below adds dates, details and sources.

The chronology, with sources

17 entries
  1. 1749Philadelphia

    Benjamin Franklin

    A “battery” of jars

    Franklin found that linking several Leyden jars let them store more charge, and he called the bank a “battery,” after a battery of cannon. He is credited as the first to use the word for electricity.2120 The jars dumped all their charge in a single spark, so this was not yet a chemical battery.

    Franklin’s battery of Leyden jars. Figuier, Les Merveilles de la science, 1867.
  2. 1791Bologna

    Luigi Galvani

    Frogs’ legs & “animal electricity”

    Galvani saw the muscles of dissected frogs twitch when they touched two different metals, and he concluded that animals carry their own “animal electricity.” He published his work as De viribus electricitatis in motu musculari.113

    Tav. I of De viribus electricitatis, 1791.
  3. 1800Como & London

    Alessandro Volta

    The voltaic pile

    Volta suspected the electricity came from the two metals, not the frog. To prove it he stacked discs of zinc and copper (silver worked even better), separated by cloth or pasteboard soaked in brine.2 Each zinc–cloth–copper layer was one cell, and adding layers added electricity. He called it an “electric organ,” and also built a “crown of cups” version using goblets of brine. It was the first device to give a steady supply of electricity.13 His letter describing it was published in the Royal Society’s Philosophical Transactions in 1800.2

    Alessandro Volta, engraved portrait published by Nicolò Bettoni.
  4. 1834London

    Michael Faraday

    Naming the parts

    In the seventh series of his Experimental Researches in Electricity, Faraday introduced electrode, anode, cathode, electrolyte and ion, the vocabulary every battery datasheet still uses.322

    Michael Faraday. William Holl the Younger after George Richmond, 1852.
  5. 1836London

    John Frederic Daniell

    The Daniell cell

    Daniell set out his copper–zinc cell in a letter to Faraday, On Voltaic Combinations, read at the Royal Society that February. It used two separate liquids, and it was built to hold a steady current far longer than Volta’s pile could.415

    A Daniell cell, cut away. Ayrton, Practical Electricity, 1891.
  6. 1859Paris

    Gaston Planté

    The first rechargeable battery

    Planté’s lead–acid cell was the first practical storage battery, and it is the direct ancestor of the battery under the hood of a car. It was a laboratory curiosity for nearly two decades before it found real use.1516

    Planté’s secondary cell on charge. Figuier, 1891.
  7. 1866France

    Georges Leclanché

    Zinc, carbon & manganese dioxide

    Leclanché replaced acid with an ammonium chloride solution and used a zinc anode with a carbon–manganese dioxide cathode packed in a porous pot. This “wet” cell gave about 1.5 volts. With only minor changes, it is the ancestor of today’s household batteries.14

    A Leclanché cell. Figuier, 1891.
  8. 1886Mainz

    Carl Gassner

    The dry cell

    In the late 1880s the electrolyte was turned into a paste, so a battery could finally be carried around without spilling. This started the dry-cell industry.15 Gassner’s U.S. patent, No. 373,064, was granted on 15 November 1887.5

  9. 1899Sweden

    Waldemar Jungner

    Nickel–cadmium

    The Swedish engineer Waldemar Jungner developed the rechargeable nickel–cadmium battery, and in 1906 he opened a factory near Oskarshamn to build it.23

  10. 1901New Jersey

    Thomas Edison

    Nickel–iron

    Edison filed a “reversible galvanic battery” patent on 20 June 1901. It was granted on 16 July as U.S. 678,722 and became the basis of his rugged nickel–iron storage battery.6

    Edison nickel–iron cell, cut away, c. 1917. Thomas Edison NHP.
  11. 1959Cleveland

    Lewis Urry, Karl Kordesch & Paul Marsal

    The alkaline battery

    The Union Carbide team filed their alkaline dry-cell patent in October 1957, and it was granted in November 1960.7 Eveready put the cell on sale in 1959.2718

  12. 1976Exxon, New Jersey

    M. Stanley Whittingham

    The first lithium battery

    Working at Exxon after the 1970s oil crisis, Whittingham used lithium ions tucked into titanium disulphide to build the first working lithium battery. It gave just over two volts, but its metallic lithium anode was too explosive to sell.118

  13. 1980Oxford

    John B. Goodenough

    Cobalt oxide doubles the voltage

    Goodenough’s group showed that lithium cobalt oxide makes a cathode of about four volts, almost twice Whittingham’s. He also realised that a battery could be built discharged and charged afterwards.911

  14. 1985Japan

    Akira Yoshino

    No more pure lithium

    At Asahi Kasei, Yoshino replaced the dangerous lithium metal with petroleum coke, which soaks up lithium ions. That made the first commercially workable lithium-ion battery, safe, light and four volts.11

  15. 1991Japan

    Sony

    Lithium-ion goes on sale

    Sony began the first industrial-scale production of lithium-ion batteries, starting a revolution in portable electronics.1711

  16. 1997Austin, Texas

    Padhi, Nanjundaswamy & Goodenough

    Lithium iron phosphate

    The team reported LiFePO4, an olivine material that takes up and releases lithium at 3.5 volts. It is now known as LFP.10

  17. 2019Stockholm

    The Royal Swedish Academy of Sciences

    A Nobel Prize

    Goodenough, Whittingham and Yoshino shared the Nobel Prize in Chemistry “for the development of lithium-ion batteries.”12

CHAPTER V

The Family of Chemistries

Each pair of materials sets its own voltage

A cell’s voltage is set by its chemistry, not its size. A huge D cell and a tiny AAA alkaline both give 1.5 volts. The table lists the nominal voltage of one cell for the chemistries you are most likely to meet.

ChemistryKindVolts / cellWorth knowing
Zinc–carbonSingle-use1.5Leclanché’s 1866 wet cell, made “dry” in the 1880s.1415
AlkalineSingle-use1.5Energizer rates the shelf life of its AA at 10 years at 21 °C.28
Lithium coinSingle-use3.0Lithium–manganese dioxide. A CR2032 loses only about 1% of its charge a year in storage.29
Lead–acidRechargeable2.0Six cells in series make a 12-volt car battery.3026
Nickel–cadmiumRechargeable1.2Industrial, aviation and military packs are rated at 1.25 V per cell.30
Nickel–metal hydrideRechargeable1.2Has the same 1.2-volt consumer rating as nickel–cadmium.30
Lithium-ion (cobalt)Rechargeable3.6Some manufacturers label the same cell 3.7 V or higher.30
Lithium iron phosphateRechargeable3.2–3.3The LFP cathode first reported in 1997.1030
Lithium titanateRechargeable2.4A lithium-ion variant whose anode is lithium titanate.30

Volta’s trick: stack them

Volta found that adding more units to his pile gave more electricity.13 Wire cells end to end, in series, and their voltages add up. Choose a chemistry and stack some cells.

Chemistry
Cells in series
6
9.0 V6 × 1.5 V alkaline

Five Bunsen cells in series, + to −. Figuier, 1867.
Fig. 4Cells in series, shown as a pile like Volta’s. The figures on the right give the running total.
Stacking at scaleThe great Wollaston battery of the Royal Institution, London, rows of cells filling a cellar. Wood engraving from Louis Figuier, Les Merveilles de la science, 1867.
CHAPTER VI · PLATE III

The Common Sizes, to Scale

D, C, AA, AAA, 9-volt & the coin cell

Common battery sizes drawn to the same scale: D 34.2 by 61.5 millimetres, C 26.2 by 50, AA 14.5 by 50.5, AAA 10.5 by 44.5, 9-volt 26.5 by 48.5, and CR2032 coin cell 20 millimetres across and 3.2 thick.

Swipe sideways to see every size.

Plate IIIAll drawn to the same scale, using the standard maximum dimensions from IEC 60086. Letters such as AA are the everyday names, and codes such as LR6 are the IEC designations for alkaline cells.242529 Inside a 9-volt you would usually find six tiny cylindrical cells.25
CHAPTER VII

Reading the Label

Volts, milliamp-hours & watt-hours

V

Volts: the push

How hard the cell pushes electrons round the circuit. It is set by the chemistry: 1.5 for alkaline, about 3.6 for lithium-ion.2830

mAh

Milliamp-hours: the tank

How much charge the cell can deliver. A 2,500 mAh cell could supply 100 milliamps for about 25 hours.27

Wh

Watt-hours: the energy

Volts multiplied by amp-hours. This is the fairest way to compare different chemistries. A 1.5 V, 2.5 Ah cell holds roughly 3.75 Wh, a little less in practice because the voltage sags as the cell drains.

The same AA, two different answers

Capacity depends on how fast you draw the current and when the device gives up. In Energizer’s own example, one AA delivers 2,500 mAh at 100 mA if the device runs it down to 0.8 volts, but only 1,500 mAh if the device quits at 1.2 volts. Batteries are generally more efficient at low drain rates.27

What the codes mean

The everyday AA is called LR6 by the IEC and 15A by ANSI.28 In IEC codes the first letter gives the chemistry (L for alkaline, C for lithium–manganese dioxide), and R means round. On a coin cell such as the CR2032, the digits give the size: 20 mm across and 3.2 mm thick.2429 That coin holds about 235 mAh at 3.0 volts and weighs 3 grams.29

CHAPTER VIII

Handling & Disposal

What goes in the bin, and what never should

The U.S. Environmental Protection Agency’s guidance, by type. Rules vary from town to town, so check with your local waste authority.31

  • Alkaline & zinc–carbonTrash is usually OKMost communities allow them in household trash. Recycling them is still better.31
  • Lithium single-use & coin cellsNever in trashTake them to a battery recycler. Tape the terminals or bag each one, and keep them away from children.31
  • Lithium-ion rechargeablesNever in trashNever put them in household trash or recycling bins. Tape the terminals or bag each battery. If a battery is built into a device, recycle the whole device.31
  • Nickel–cadmium & NiMHNever in trashUse a battery recycler, a store take-back program or household hazardous-waste collection.31
  • Lead–acid (car)Never in trashReturn it to a battery retailer or hazardous-waste program. It contains sulfuric acid and lead.31
CHAPTER IX

Sources

Where every fact on this page comes from

Each small numeral on this page links here. Original papers and patents come first, then the museums, prize committees and reference works that explain them, then the manufacturer data sheets and safety agencies. Where sources disagree, the text says so.

Primary documents

  1. 1Galvani, L. (1791). De viribus electricitatis in motu musculari commentarius. Bologna. Digitised at Internet Archive.
  2. 2Volta, A. (1800). “On the Electricity excited by the mere Contact of conducting Substances of different Kinds.” Philosophical Transactions of the Royal Society of London 90: 403–431. doi:10.1098/rstl.1800.0018
  3. 3Faraday, M. (1834). “Experimental Researches in Electricity. Seventh Series.” Phil. Trans. R. Soc. Lond. 124: 77–122. doi:10.1098/rstl.1834.0008
  4. 4Daniell, J. F. (1836). “On Voltaic Combinations. In a letter addressed to Michael Faraday.” Phil. Trans. R. Soc. Lond. 126: 107–124. doi:10.1098/rstl.1836.0012
  5. 5Gassner, C., Jr. (1887). Galvanic Battery. U.S. Patent 373,064, granted 15 Nov. 1887. Google Patents
  6. 6Edison, T. A. (1901). Reversible Galvanic Battery. U.S. Patent 678,722, filed 20 June, granted 16 July 1901. Google Patents
  7. 7Marsal, P. A., Kordesch, K. & Urry, L. F. (1960). Dry Cell. U.S. Patent 2,960,558, filed 9 Oct. 1957, granted 15 Nov. 1960, assigned to Union Carbide. Google Patents
  8. 8Whittingham, M. S. (1976). “Electrical Energy Storage and Intercalation Chemistry.” Science 192 (4244): 1126–1127. doi:10.1126/science.192.4244.1126
  9. 9Mizushima, K., Jones, P. C., Wiseman, P. J. & Goodenough, J. B. (1980). “LixCoO2 (0<x≤1): A new cathode material for batteries of high energy density.” Materials Research Bulletin 15 (6): 783–789. doi:10.1016/0025-5408(80)90012-4
  10. 10Padhi, A. K., Nanjundaswamy, K. S. & Goodenough, J. B. (1997). “Phospho-olivines as Positive-Electrode Materials for Rechargeable Lithium Batteries.” J. Electrochem. Soc. 144 (4): 1188–1194. doi:10.1149/1.1837571

Institutions & references

  1. 11The Royal Swedish Academy of Sciences (2019). “They developed the world’s most powerful battery.” Popular science background, Nobel Prize in Chemistry 2019. nobelprize.org
  2. 12The Royal Swedish Academy of Sciences (2019). Press release: The Nobel Prize in Chemistry 2019. nobelprize.org
  3. 13National High Magnetic Field Laboratory. “Voltaic Pile – 1800.” Magnet Academy, History of Electricity & Magnetism. nationalmaglab.org
  4. 14National High Magnetic Field Laboratory. “Leclanché Cell – 1866.” Magnet Academy. nationalmaglab.org
  5. 15Encyclopaedia Britannica. “Battery: Development of batteries.” britannica.com
  6. 16Engineering and Technology History Wiki (IEEE). “Gaston Planté.” ethw.org
  7. 17IEEE Milestones. “Milestone-Proposal: Lithium-Ion Battery, 1985.” Engineering and Technology History Wiki. ethw.org
  8. 18Lemelson-MIT Program. “Lewis Urry.” lemelson.mit.edu
  9. 19Argonne National Laboratory (U.S. DOE). “Science 101: Batteries.” anl.gov
  10. 20Wilton, D. “battery (electrical).” Wordorigins.org. wordorigins.org
  11. 21Smithsonian Institution. “Benjamin Franklin’s Pioneering Electrical Work Influenced Today’s Technology.” Newsdesk release, National Museum of American History. si.edu
  12. 22Harper, D. “anode.” Online Etymology Dictionary. etymonline.com
  13. 23Wikipedia. “Waldemar Jungner.” wikipedia.org
  14. 24Wikipedia. “List of battery sizes” (dimensions per IEC 60086). wikipedia.org
  15. 25Wikipedia. “Nine-volt battery.” wikipedia.org
  16. 26Wikipedia. “Automotive battery.” wikipedia.org

Technical data & safety

  1. 27Energizer Brands (2018). Alkaline Manganese Dioxide Handbook and Application Manual. data.energizer.com (PDF)
  2. 28Energizer Brands. Energizer E91 (AA, LR6) Product Datasheet. data.energizer.com (PDF)
  3. 29Energizer Brands. Energizer CR2032 Lithium Coin Product Datasheet. data.energizer.com (PDF)
  4. 30Battery University (Cadex Electronics). “BU-303: Confusion with Voltages.” batteryuniversity.com
  5. 31U.S. Environmental Protection Agency. “Used Household Batteries.” epa.gov
  6. 32National Capital Poison Center. “Swallowed a Button Battery? Battery in the Nose or Ear?” poison.org

Illustrations

  1. Plates I & II (Inside a Modern Battery; The Invention of Batteries): illustrations made for Kreindo.
  2. Plate III, Figs. 2–4: drawn for this page from the dimensions and data cited above.
  3. Fig. 1: Volta's own 1800 plate showing the crown of cups (Fig. 1) and three voltaic-pile arrangements of zinc/silver discs (Figs. 2-4). Alessandro Volta (plate engraved by Basire for Phil. Trans.; digital cleanup by en:User:Kurzon), 1800. Public domain (PD-old), via Wikimedia Commons.
  4. Chronology, 1800: Oval line-engraved bust portrait of Alessandro Volta wearing his orders, lettered 'Alessandro Volta'. Published by Nicolò Bettoni (plate inscribed 'Per Nicolò Bettoni'); engraver not named, Early 19th century (undated on Commons). Public domain (PD-old), via Wikimedia Commons.
  5. Chronology, 1791: Tav. I of De viribus electricitatis in motu musculari: an electrostatic machine, a Leyden jar and prepared frog legs on a laboratory table. Luigi Galvani (plate engraved by J. Zambelli), 1791. Public domain (PD-old-auto-expired), via Wikimedia Commons.
  6. Chronology, 1749: Franklin's electrical battery: a box of linked Leyden jars with a quadrant electrometer, which Figuier calls an exact copy of a plate from Franklin's own memoir. Louis Figuier, Les Merveilles de la science, vol. 1 (after the plate in Franklin's Œuvres, trans. Barbeu-Dubourg, 1773), 1867. Public domain (PD-old-100-1923), via Wikimedia Commons.
  7. Chronology, 1836: Cutaway engraving of a Daniell cell with copper cylinder (C), porous pot (P) and zinc rod (Z) inside a stoneware jar (J). William Edward Ayrton, Practical Electricity (fig. 76), 1891. Public domain (PD-old), via Wikimedia Commons.
  8. Chronology, 1859: Planté's lead secondary cell being charged by two Bunsen cells, beside a cased cell opened to show its rolled lead sheets. Louis Figuier, Les Merveilles de la science, vol. 5 (wood engraving signed A. Jahandier / C. Laplante), 1891. Public domain (PD-old-100-1923), via Wikimedia Commons.
  9. Chronology, 1866: Leclanché cell of the agglomerate type: pressed manganese-dioxide blocks strapped to a carbon plate, with a zinc rod, in a glass jar. Louis Figuier, Les Merveilles de la science, vol. 5, 1891. Public domain (PD-old-100-1923), via Wikimedia Commons.
  10. Chronology, 1901: Labelled black-and-white cutaway of an Edison nickel-iron alkaline cell showing nickel-hydrate positive tubes, iron-oxide negative pockets and a steel case. Edison Storage Battery Company artwork; photographed by U.S. National Park Service (Thomas Edison National Historical Park), c. 1917 (same artwork appears in a 1917 Edison brochure); NPS photograph 2011. Public domain (PD-USGov-NPS), via Wikimedia Commons.
  11. Chronology, 1834: Stipple-engraved bust portrait of Michael Faraday on cream paper. William Holl the Younger, after George Richmond (Metropolitan Museum of Art, 2013.86), 1852. CC0, via Wikimedia Commons.
  12. Chapter V: The great Wollaston-type trough battery built for Humphry Davy, filling a vaulted cellar at the Royal Institution in London. Louis Figuier, Les Merveilles de la science, vol. 1 (wood engraving signed L. Guiguet), 1867. Public domain (PD-old-100-1923), via Wikimedia Commons.
  13. Chapter V: Five Bunsen carbon-zinc cells wired in series, with + (carbon) and - (zinc) ends marked. Louis Figuier, Les Merveilles de la science, vol. 1, 1867. Public domain (PD-old-100-1923), via Wikimedia Commons.