Electric battery

• 1. Introduction

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  An electric battery is a source of electric power, built from one or more electrochemical cells with external connections that feed electrical devices. When it supplies power, its positive terminal is the cathode and its negative terminal is the anode. From that negative terminal, electrons stream out. They travel through a connected circuit, reach the positive terminal, and drive a redox reaction by attracting positively charged ions. Higher energy reactants become lower energy products. The free-energy difference left over arrives in the external circuit as electricity. The word itself is older than that tidy explanation. It once meant a device of multiple cells, then stretched to cover even a single cell. So where did the term come from, and who first made one steady enough to matter? Why does a chemistry built for flashlights also stabilize an electrical grid? And why, after two centuries, can a battery still kill a child or burst into flame on a workbench? The answers run from a set of linked jars in the 1700s to battery banks the size of rooms.

• 2. Naming The Charge

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  Benjamin Franklin reached for a military word in 1749. Experimenting with linked Leyden jar capacitors, he grouped several jars together and called the cluster a "battery", borrowing the term for weapons working in concert. Stacking more holding vessels stored a stronger charge, and discharge released more power.

  Alessandro Volta, an Italian physicist, built and described the first electrochemical battery in 1800. His voltaic pile stacked copper and zinc plates separated by brine-soaked paper disks, and it produced a steady current for a considerable length of time. Volta misread his own invention. He believed the cells were an inexhaustible source of energy, and treated the corrosion at the electrodes as a nuisance rather than a necessary cost of operation.

  Michael Faraday corrected that belief in 1834, showing the corrosion was unavoidable. Even so, early batteries delivered fluctuating voltages and could not sustain a large current for long. The fix arrived in 1836, in a copper pot that would carry messages across a continent.

• 3. Wet Cells And Dry Cells

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  The Daniell cell, invented in 1836 by British chemist John Frederic Daniell, became the first practical source of electricity. It was a copper pot filled with copper sulfate solution, holding an unglazed earthenware container of sulfuric acid and a zinc electrode. It turned into an industry standard and powered electrical telegraph networks.

  Liquid electrolytes carried a hidden cost. These wet cells leaked and spilled when mishandled, and many sat in glass jars that made them fragile and dangerous. Such traits ruled wet cells out for portable appliances. The standard dry cell answered with a zinc anode shaped as a cylindrical pot and a central carbon cathode rod. Its electrolyte is ammonium chloride paste beside the zinc, with a second paste of ammonium chloride and manganese dioxide filling the rest, the manganese dioxide acting as a depolariser.

  Near the end of the nineteenth century, dry cell batteries replaced the liquid electrolyte with a paste and made portable electrical devices practical. A dry cell holds no free liquid, so it works in any orientation without spilling. Vacuum tube devices once mixed both worlds, using a wet cell for the "A" battery to heat the filament and a dry cell for the "B" battery to supply plate voltage. The lead-acid battery would not match the dry cell's safety and portability until the gel battery arrived.

• 4. Inside A Cell

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  Batteries convert chemical energy directly into electrical energy, and the released energy is often the difference in bond energies of the metals or molecules in the reaction. Zinc and lithium store a lot of it. They are high-energy metals precisely because they lack the d-electron bonding that stabilizes transition metals.

  Each cell holds two half-cells joined in series by a conductive electrolyte carrying metal cations. Cations are reduced at the cathode while metal atoms are oxidized at the anode. When two electrolytes differ between the half-cells, a separator blocks mixing while still letting ions flow to complete the circuit.

  Every half-cell has an electromotive force measured in volts, and the cell's net emf is the difference between the two half-cell emfs. A cell that is neither charging nor discharging shows its open-circuit voltage, which equals the emf. Internal resistance bends those numbers. A discharging cell reads below its open-circuit voltage, a charging cell reads above it, and an ideal cell holding 1.5 volts and producing one coulomb would perform 1.5 joules of work before dropping to zero.

  Chemistry sets the voltage. Alkaline and zinc-carbon cells differ in makeup yet both land near 1.5 volts, while NiCd and NiMH cells both sit near 1.2 volts. Lithium compounds push higher, giving lithium cells emfs of 3 volts or more. The principle is loose enough that two coins and a salt-soaked paper towel can form a working voltaic pile.

• 5. From Button Cells To Battery Banks

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  Button cells power electric watches at one end of the size range, and the No. 6 cell handles signal circuits and other long-duration jobs. Secondary cells scale up far past that, large enough to run a submarine or to stabilize an electrical grid and level out peak loads.

  Tesla built the world's largest battery in South Australia, able to store 129 MWh. A battery in Hebei Province, China, storing 36 MWh, was built in 2013 at a cost of $500 million. Another, made of Ni-Cd cells, sat in Fairbanks, Alaska, covering 2000 square metres, weighing 1,300 tonnes, and built by ABB to supply 40 MW of backup power for up to seven minutes after a blackout. A 4.4 MWh sodium-sulfur system that delivers 11 MW for 25 minutes steadies the output of the Auwahi wind farm in Hawaii.

  The lead-acid battery is the oldest rechargeable form, widely used in automotive and boating settings. It holds liquid electrolyte in an unsealed container, so it must stay upright in a ventilated space to release the hydrogen gas it makes during overcharging. Heavy for the energy it stores, it survives on low cost and high surge current, and a modern car battery can deliver a peak of 450 amperes.

• 6. Capacity And Decline

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  Capacity is the charge a battery can deliver while staying above its specified terminal voltage, and more electrode material means more of it. The figure is usually given in ampere-hours, set as 20 hours times the current a new battery can supply for 20 hours at 20 C. A battery rated at 100 A·h delivers 5 A across that 20-hour stretch.

  Discharge rate cuts into the total. For a lead-acid battery, Peukert's law approximates how current, time, and capacity trade off, with a constant around 1.3. High-drain loads like digital cameras pull capacity down further, so a cell rated at 2 A·h over a 10- or 20-hour discharge will not hold 1 A for a full two hours. The C-rate captures this, dividing the current by the draw that would empty the nominal capacity in one hour.

  Charged batteries bleed away on their own. Disposable batteries lose 8 to 20% of their charge per year stored at 20 to 30 degrees Celsius, through side reactions that consume charge carriers without producing current. A freshly charged NiCd loses 10% in the first 24 hours, then roughly 10% a month, while newer NiMH and lithium designs self-discharge more slowly. Lower temperatures slow these reactions, though storing in a fridge risks damaging condensation.

  Each cycle wears the plates as electrolyte migrates or active material detaches. Low-capacity NiMH cells of 1,700 to 2,000 mA·h take about 1,000 charges, high-capacity cells above 2,500 mA·h last around 500, and NiCd cells rate near 1,000 cycles. Vibration, shock, and lead-plate sulfation mean few automotive batteries survive beyond six years. The Zamboni pile, invented in 1812, defies all of this, running for a very long time on tiny nanoamp currents.

• 7. When Batteries Turn Dangerous

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  A battery explosion usually traces to misuse or malfunction, such as recharging a primary cell or a short circuit. Charge a battery too fast and an explosive mix of hydrogen and oxygen builds faster than it can vent, pushing pressure up until the case bursts and chemicals spray out. Car batteries are most likely to explode when a short circuit drives very large currents, and jump-starting can release enough hydrogen to ignite from a nearby spark when a jumper cable comes off.

  Many battery chemicals are corrosive, poisonous, or both. Disposable batteries often use a zinc "can" as both reactant and container, and over-discharge can push the reagents through the cardboard and plastic shell, damaging the equipment they power. Device makers often advise pulling batteries out of gear that will sit unused.

  Swallowing a battery can be fatal. Small button cells are easy for young children to swallow, and the battery's electrical discharge can damage tissue. The esophagus is the most common lodging point, where sodium hydroxide generated at the anode can cause liquefaction necrosis, with perforation seen as soon as 6 hours after ingestion. Older children usually pass batteries smaller than 21 to 23 mm without trouble. Some manufacturers now add a bittering agent to discourage swallowing.

  Toxic lead, mercury, and cadmium make disposal its own hazard. Of the nearly three billion batteries bought each year in the United States, about 179,000 tons reach landfills. E-waste recycling recovers those toxic substances for new batteries, and that recovered material feeds the demand the next chapter measures.

• 8. A Surging Industry

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  Battery demand grew 30% annually between 2010 and 2018, reaching 180 GWh in 2018. Held at an estimated 25%, that growth points to 2600 GWh by 2030, and cost reductions could push it as high as 3562 GWh. The drivers are the electrification of transport and large-scale deployment in electricity grids, backed by decarbonization efforts.

  Distributed batteries now act inside smart grids, from battery electric vehicles feeding power back through vehicle-to-grid to home energy storage with smart metering and demand response. Vehicles whose batteries drop below 80% capacity, usually after 5 to 8 years, get repurposed for backup supplies or renewable energy storage, stretching their service life and trimming costs.

  Laboratories keep reaching further. On the 28th of February 2017, the University of Texas at Austin announced a solid-state battery from a team led by lithium-ion inventor John Goodenough, claimed to hold three times the energy density and to use cheaper, earth-friendly materials such as sodium extracted from seawater. Sony built a biological battery that draws electricity from sugar using enzymes that break down carbohydrates. In 2024 a prototype car battery charged from 10% to 80% in five minutes, and a Chinese company claimed a 10.5-minute version, the fastest available, against Tesla's 15 minutes to half-charge.

  Regulators are reshaping the object itself. On the 9th of December 2022, the European Parliament agreed to require, from 2026, that manufacturers design electrical appliances sold in the EU so consumers can remove and replace the batteries themselves.