BU-1101: Glossary

Discover easy-to-understand explanations of technical battery terms.

AC:  Alternating current; current flows in both directions. Household current is AC.

Acid: Compound in a battery that promotes electrochemical reaction.

AGM:  Absorbent Glass Mat is a lead acid battery that uses a glass mat to promote the recombination of gases produced by the charging process.

Allotrope:  Two or more forms of the same element in the same physical state (solid, liquid, gas) that differ from each other in physical and sometimes chemical properties.

Ampere-hours: Symbol Ah is a unit of charge. Example: Drawing a current of one ampere (1A) from a battery for one hour (1h) equates in one ampere-hour (1Ah).

Anode:  Electrode on which oxidation occurs; releases electrons on discharge. When applying power to a device (vacuum tube, diode, battery on charge), the anode is positive; taking power away on discharge turns the anode to negative.

Antimony: Used in lead acid batteries to improve mechanical strengths of lead plates and enhances performance. Other uses are flame proofing, producing low friction applications, and building semiconductors.

Barrel: Measuring unit for liquids (oil); 1 barrel has 42 US gallons, 35 Imperial gallons, 159 liters.

Basel Convention: International treaty to reduce the movements of hazardous waste between nations; signed in1989 in Basel, Switzerland and made effective in 1992.

Battery: Electrochemical cell, or cells, connected in series (some in parallel); composed of the anode (negative electrode), cathode (positive electrode), separator and electrolyte as catalyst.

Battery cycle:  Charge followed by a discharge and recharge. No standard exists as to level of charge and discharge to constitute a cycle.

Battery Directive 2006/66/EC: European legislation on waste batteries to protect the environment.

BMS: Battery Management System used inside or outside a battery to manage charge, discharge and provide SoC; forms an essential part to assure battery longevity and safety.

Bluetooth:  Low-power radio communications up to 10 meters (30 feet). Bluetooth borrowed the name from Harald Bluetooth, a Danish king who lived more than 1,000 years ago.

Boolean bit:  System of symbolic logic devised by George Boole in the 1840s; used in computers.

Button cell:  Miniaturized battery also known as coin cell. Most are non-rechargeable.

Calcium:  Fifth most abundant element by mass in the earth crust; essential for living organisms to build bone, teeth and shells. Discovered by Humphry Davy (1778–1829). Improves mechanical strength of lead plates in lead acid batteries; enhances performance.

Candela (cd): Unit of luminous intensity; agreed international name since 1967.

Capacitance:  Unit measuring the electrical charge in a capacitor (condenser), measured in farad (f).

Capacitor:  Component consisting of two conductive surfaces separated by an insulator. Passes AC; indefinite resistance for DC; voltage lags behind the current (opposite of a coil). 

Capacity: Electrical energy of a battery in ampere-hours (Ah). The stored energy is measured by observing the elapsed time while discharging at a constant current to the end-of-discharge voltage. The capacity is the leading health indicator of a battery.

Capacity offset: Capacity correction when discharging a battery at a higher C-rate than specified.

Carbon dioxide: (CO2) Odorless gas formed during combustion, respiration and decomposition of organic substances. Plants absorb CO2; excess CO2 is blamed for climate change.

Cathode:  Electrode in an electrochemical cell in which reduction takes place by absorbing electrons. During discharge, the cathode is positive; reverse on charge.

C-code:  Abbreviation for  configuration code. C-code is stored in a battery adapter and configures the analyzer to the correct battery settings (Cadex systems).

Cell mismatch:  Cells in a battery pack that have unequal capacities, voltages or resistive values.

Cell reversal:  Cell polarity reverses on a deep discharge at high load. Damages affected cell.

Charge: Replenishing electrical charge to a cell or battery.

Chemical battery: Behavior of the actual battery as opposed to monitoring peripheral activities.

Cobalt (Co): Hard, lustrous, gray metal; used in batteries, magnets, and high-strength alloys.

Co-generation: Utilization of heat and kinetic force. Heat drives steam turbines; kinetic force produces electricity through a generator; charges a battery on deceleration.

Coke: Derivative of coal from which most gases have been removed through heating.

Coulomb: Unit of electric charge. One coulomb (1C) per second is one ampere (1A).

Coulombic efficiency, also called faradaic efficiency or current efficiency describes the charge efficiency by which electrons are transferred in a batteries.

C rate:  Unit by which charge and discharge times are scaled. At 1C, the battery charges and discharges at a current that is at par with the marked Ah. (See BU-402)

Current-limiting charger: Keeps current constant and allows voltage to fluctuate. (NiCd, NiMH chargers)

Cycle:  Charge/discharge/charge. No standard exists as to what constitutes a cycle.

Cycle life: Number of cycles a battery can deliver. (End of-battery-life for portable devices is commonly set to 80%.)

Cylindrical cell: Positive and negative plates are rolled up and placed into a cylindrical container.

DC:  Direct current; current flows in one direction. A battery delivers a DC current.

DC-to-DC converter: Converts DC to a higher or lower voltage potential.

Delta temperature over delta time (dT/dt): Senses rate of temperature increase over a given time rather than by measuring the absolute value; used for full charge detection of nickel-based battery. (See BU-407)

Digital battery: Peripheral that monitors battery activity associated with the smart battery.

DIN, IEC:  Capacity of a starter battery is measured with a 0.2C-rate (5h) discharge of a fully charged battery to 1.55V/cell or a 0.05 (20h) discharge to 1.75V/cell.

DoD:  Depth of discharge; 100% is full discharge; 80% is commonly used for specification.

Double-layer capacitor: Electrostatic storage device utilizing the electrical double layer effect that is formed near the surface of the carbon electrode; also called supercapacitors or ultracapacitors.

Driving range: EVs display the allowable driving rang range rather than capacity. As the capacity fades, battery gets charged more and discharged deeper. The full capacity is hidden.

Dumb battery: Basic electrochemical battery with no electronic intelligence with which to communicate.

Electrochemical impedance spectroscopy (EIS), also known as impedance spectroscopy; method to test electrochemical characteristics of a battery; EIS injects AC signals at different frequencies and analyzes the response. (See BU-904)

Electrode:  Conductor or plate in a cell in which an electrochemical reaction occurs.

Electrolyte: Non-metallic conductor of electricity (typically liquid) placed between positive and negative electrodes of a battery. Ion movement enables current flow.

Electrolyte oxidation (EO): Formation of a restrictive film on the Li-ion cathode if the voltage is kept above 4.10V/cell. The longer the battery stays in a high voltage, the more pronounced the degradation will be.

Energy: Work measures over time. Multiplying voltage x current x time = Watt-hours (Wh). Energy is also given in joules (J); 1,000 joules are 0.277Wh.

Energy Cell: Battery cell designed for maximum capacity. Power density may be compromised.

Energy density: Also known as volumetric energy density; specifies the amount of energy a cell can hold in volume (Wh/l). Energy density is synonymous with the runtime of a battery.

Energy Star: Organization promoting energy efficiency.

Exercise: In battery maintenance, one or several discharge cycles to the end-of-discharge with recharge; prevents memory buildup in NiCd and NiMH batteries.

Farad (f): Charge in coulombs necessary to change the potential between the plates of a capacitor by 1V. (1 Farad = 1 Coulomb per Volt)

Fast charge:  1–3 hours charge time.

Float charge: Similar to trickle or maintenance charge; compensates self-discharge of lead acid battery.

Flow battery: A cross between a conventional battery and a fuel cell. Liquid electrolyte of metallic salts is pumped through a core with positive and negative electrodes, separated by a membrane. The resulting ion exchange generates electricity. (See BU-210b)

Frequency: Number of events in a given time. Indicates how often the AC voltage changes from positive to negative per second, or how many times a battery is cycled.

Fuel cell: Device converts oxygen and hydrogen into electricity and water. (See BU-210)

Fuel gauge: State-of-charge (SoC) indicator to estimate the charge level of a battery.

Fuzzy logic: Multi-valued, mathematical logic derived from blurred data derives at a voted result. Battery rapid testing, image recognition, weather forecasting and medical tests follow fuzzy logic.

Graphene: Allotrope of carbon in a two-dimensional hexagonal lattice in which one atom forms each vertex; establishes the basic structural element of graphite, charcoal diamonds and more.

Graphite: A form of carbon with hexagonally crystallized allotrope, used in lead pencils, lubricants, batteries and the anode of most Li-ion.

Gravimetric energy density: Also known as specific energy; indicates the amount of energy a cell holds in weight (Wh/kg); synonymous with battery runtime.

Halon: Agent to suppress fire. Used also for Li-ion fires.

Hertz (Hz): Unit of frequency; 1Hz constitutes one full cycle per second.

Hydrogen (H): Chemical element with atomic number 1; lightest and most abundant chemical element; constitutes roughly 75% of the universe's elemental mass. Hydrogen gas becomes explosive at a concentration of 4 percent.

Hydrometer: Device to measure the specific gravity of a fluid; reads state-of-charge of a lead acid and other flooded batteries.

Hysteresis charge: Charger turns off at full charge and resumes after a time to compensate for parasitic loads and self-discharge.

I2C:  Inter-Integrated Circuit is a multi-master, multi-slave, single-ended, serial computer bus invented by Philips Semiconductor.

IEC 60079: Intrinsically safe standards to prevent explosion in areas of flammable gas and dust.

IEC 60086: Safety standard for primary batteries.

IEC 62133: Safety requirements for sealed secondary cells/batteries for portable use. 

IEEE 1625: Standard for rechargeable batteries for mobile computing devices.

IEEE 1725: Standard for rechargeable cells/batteries for mobile phones.

Imaginary impedance: Also known as complex impedance; characterizes the electrical resistance of reactive components as a function of frequency. Rising frequency lowers the capacitive resistance and increases the inductance resistance.

Impedance: Combination of capacitive, inductive and ohmic resistance; measured in ohms (R); frequency dependent.

Inductance (L): Winding that causes an electromotive force when current is applied; frequency dependent; reacts opposite to a capacitor; measurement in Henry (H. 

Intelligent battery: Also known as smart battery; enables communication between device, charger and user.

Internal resistance: Electrical resistance of a battery pack in milliohms (m). A good battery has low resistance; corrosion raises it.

Intrinsically safe battery: Has built-in protection circuit to enable safe operation in a hazardous area; prevents sparks by limiting voltage and current spikes.

Ion:  Atom or molecule with unequal number of electrons and protons; provides a positive or negative electrical charge.

Joule (J): Energy measurement: 1 joule = 1A at 1V for 1 second. Also applies to mechanical energy.

Lead acid battery: Oldest rechargeable battery; used as starter battery wheeled mobility, UPS, etc.

Lithium (Li): Soft, silver-white metal belonging to the alkali metal group; lightest and least dense metal in the element family; discovered by Johan August Arfwedson in 1817; metal is named after the Greek word “lithos” meaning “stone.”

Lithium battery: Has lithium-metal anode; most are non-rechargeable.

Lithium-ion battery: Rechargeable battery with cobalt, manganese, nickel and/or other metals as cathode and graphite anode.

Lithium-ion polymer battery: Similar to Li ion with a solid polymer as electrolyte; addition of gelled material promotes conductivity.

Lithium polymer battery: Also known as solid-state battery; uses solid polymer as electrolyte; heat induces conductivity.

Load current: Current flow when applying an electrical load.

Manchester coding, also known as phase coding, is used in 1-Wire battery communications to combine data and clock in a single-wire system 

Manganese (Mn): Cathode material of Li-ion. Also used in steelmaking.

Matrix:  Lookup table to compare and derive at characteristics, such as battery capacity.

Max Error: Expected margin of error (%) of charge calibration on SMBus battery.

Memory:  Reversible capacity loss in nickel-based batteries.

Microsecond (μs): One-millionth of a second (10-6).

Milliampere-hour (mAh): Specifies battery capacity or rating; 1000mAh equals 1Ah.

Millihertz: Unit of frequency. Example: 1 Hertz = 1 cycle/second; 1mHz = 1,000 seconds.

Millisecond (ms): One-thousand of a second (10-3).

Nano:  Latin for dwarf. 1 nanometer (nm) is one-billionth (10-9) of a meter or a layer of 3–6 atoms.

NCA:  Nickel-cobalt-aluminum Li-ion; serves as cathode material.

Negative delta V (NDV): Drop in battery voltage when sealed NiCd and NiMH reach full charge; used to detect full charge.

Newton (N):  Unit of force named after Isaac Newton; equal to accelerating 1kg a distance of 1 meter per second; (1N = 0.2248 pounds of force).

Nickel-cadmium battery (NiCd): Rechargeable battery using cadmium as anode and nickel as cathode.

Nickel-hydrogen battery (NiH): Rechargeable battery for satellites; pressure vessel contains the hydrogen.

Nickel-iron battery (NiFe): Rechargeable battery developed by Thomas Edison in 1901.Used for mining; powered German V-1 flying bomb and the V-2 rockets during World War II.

Nickel-metal-hydride battery (NiMH): Similar to NiCd; anode made of a hydride alloy that is less toxic than cadmium; 30 percent more capacity than NiCd but is less durable.

Nickel-zinc battery (NiZn): Similar to NiCd; first developed in 1920; short life due to dendrite growth.

Nit: Unit of brightness equal to one candela per square meter.

NMC:   Lithium-ion with nickel, manganese and cobalt as cathode material.

Nominal voltage: Terminal voltage of batteries.

Nyquist plots:  Invented by Harry Nyquist (1889–1996) while working at Bell Laboratories; provides the  frequency response of a linear system that displays both amplitude and phase angle on a single plot using frequency as parameter.

Ohmic resistance: Electrical DC resistance with no capacitive and inductive reactance.

OhmTest™: Battery resistance measurement based on IEC 61951 (Cadex trademark).

Organic: Relating or belonging to carbon-based chemical compounds. Also relates to an organism, a living entity. Organic matter is the product of decay from a once living organism

Overcharge: Exceeding charge acceptance. The battery heats up, produces gases and is subject to an evet.

Overpack: Package can contain other non-dangerous or compatible dangerous good items. Limit is one package in accordance with Section II of PI 965. (Effective 1 April 2016).

Parasitic load: Power consumption with the device turned off.

Passivation layer: Resistive layer that forms on some batteries after prolonged storage. Applying a brief load breaks the layer and enables current flow.

Peukert law: Calculates battery capacity on discharge rate; higher rates decrease capacity. Mainly used for lead acid batteries; a reading close to 1 indicates a battery with minimal loss; larger number reflect higher losses; named after Wilhelm Peukert (1897).

Phosphate: Salt or phosphoric acid.

Polymer: Electrical insulator that passes ions.

Pouch cell: Packaged into a flexible, heat-sealable foil pouch similar to wrapping food products.

Power:  Voltage x current = power in watts (W). Also in horsepower (1hp = 746W).

Power Cell: Battery cell designed for maximum current delivery. Energy density may be compromised.

Power density: Also known as volumetric power density; reflects loading capability of a battery.

Power factor:  Ratio of real power versus apparent power. The unity power factor of 1 delivers 100% current to a load; a power factor of 0.50 reduces the contribution to 50%. A purely resistive load (heater elements) has a unity power factor of 1; a purely capacitive or inductive load has a power factor of 0.

Primary battery: Non-rechargeable battery.

Prismatic cell: A battery in which the positive and negative plates are stacked instead of rolled.

Protection circuit: Electronic circuit in a battery pack maintains safety when exceeding design limits.

Quick charger: Charges a battery in 3–6 hours.

QuickSort™: Classifies battery state-of-health into good, low and poor (Cadex trademark).

QuickTest™: Method to quick-test battery state-of-health (Cadex trademark).

Ragone chart: Plots battery performance on specific energy versus specific power

Randles Model: Equivalent electrical circuit representing electrolyte resistance in a battery that is commonly used in electrochemical impedance spectroscopy (EIS).

Rapid charge: Same as quick charge.

Reactance: Inductive and capacitive resistance; frequency dependent.

Recondition: Secondary discharge applied after end-of-discharge to drain the battery further; helps break down crystalline formation (memory) of nickel-based batteries. (See BU-807)

Reformer: Device that extracts hydrogen from fossil and other fuels.

Reserve Capacity: American way of measuring battery capacity by applying a fixed discharge current and measuring time in minutes. Europe uses the ampere-hour (Ah) method under DIN and IEC. DIN and IEC mark the battery in Ah at a typical discharge of 0.2C-rate (5h-rate). See Abbreviation.

Residual capacity: Remaining battery capacity before charge.

Resistance: Restriction to current flow; high resistance generates voltage drop and heat.

Reverse load charge: Intersperses discharge pulses between charge pulses to promote the recombination of gases generated during fast charge; reduces memory.

Runtime:  The length of time a battery provides power with a charge.

SAE J537: Test standard for 12V automotive starter batteries.

RC: Apply a full charge (charge to 14.4–16V at 16°C–43°C (60°F–110°F)). After a 24h rest, apply a regulated 25A discharge to 10.50V (1.75V/cell). Readings are in minutes of discharge time known as “Reserve Capacity” (RC).

CCA: Fully charge the battery and cool to -18C (0F) for 24 hours. While cold, apply a discharge current equal to the specified CCA reading. To pass, the voltage must stay above 7.2V (1.2V/cell) for 30 seconds. [Line up RC and CCA with the first line]

SAE J1634:  Test standard for electric vehicle; energy consumption, range.

SAE J1772: North American standard for electrical connectors for electric vehicles.

Secondary battery: Rechargeable battery

Self-discharge: Capacity loss due to internal leakage.

Separator: Isolates cathode and anode in a battery; acts as catalyst to promote ion movement from cathode to anode on charge and in reverse on discharge.

Siemens (s): Unit of electric conductance; equal to reciprocal ohm. Named after Ernst Werner von Siemens (1816–1892).

Silver-zinc: Rechargeable battery with high specific energy for defense and aerospace; has a short cycle life; is expensive. 

Single-wire Bus: Simplified smart battery with one wire providing digital communications.

Slow charge: Overnight charge lasting 10–16 hours at a charge current of 0.1C.

Smart battery: Also known as an intelligent battery; communicates with device, charger and user.

SMBus: System Management Bus is a two-wire interface based on I2C; communicates with the battery and device by accepting control parameters and providing battery status, such as state-of-charge, manufacturer information, cycle count and error messages.

Sodium-nickel-chloride: Further development of sodium-sulfur battery. Zeolite Battery Research Africa Project (ZEBRA) made the battery commercially viable; must be heated for operation, used for large UPS and EVs.

Sodium–sulfur (NaS): Molten-salt battery; gained attention in 1970s, 1980s; has a short service life and high manufacturing costs; superseded by the sodium-nickel-chloride battery.

Soft cell: High cell resistance. The voltage drops on a load and is unable to clamp on charge. Very cold temperature and lack of electrolyte causes this condition.

Solid electrolyte interface (SEI): A film composed of lithium oxide and lithium carbonate forms on the surface of the Li-ion anode. The SEI layer grows with cycling and can form a barrier to obstruct ion flow.

Sol: Used by planetary astronomers to refer to the duration of a solar day on Mars. A Mars solar day has a mean period of 24 hours 39 minutes 35.244 seconds.

Specific energy: Also known as gravimetric energy density; indicates the amount of energy a cell contains in weight (Wh/kg); relates to battery capacity; governs runtime.

Specific gravity (SG): Weight ratio of a chemical solution compared to water at a specified temperature. SG of water is 1.0; the electrolyte of a fully charged lead acid battery is about 1.30.

Specific power: Also known as gravimetric power density; reflects the loading capability or the amount of current the battery can deliver; readings in W/kg.

Spectro™: Multi-model electrochemical impedance spectroscopy. Scans battery with a frequency and compares the signatures against matrices representing various conditions. (Cadex trademark) (See BU-904)

Spectroscopy: Analysis of a compound or a battery when scanned with a frequency.

Spinel: Hard glassy mineral consisting of an oxide of magnesium and aluminum that forms a three-dimensional chemical structure. Manganese-based Li ion has such a spinel structure.

State-of-charge (SoC): Indicates charge level of a battery; normally measured in percent. SoC has no relationship with capacity. 

State-of-function (SoF): Reflects battery readiness that verifies capacity, current delivery, voltage, SoC, self-discharge and more; measured in %. (Capacity, current delivery and SoC are most basic.)

State-of-health (SoH): Reflects battery performance that verifies capacity, current delivery, voltage and self-discharge; measured in %. SoH excludes SoC.

Sulfation: Formation of lead sulfate crystal in a lead acid battery that inhibits current flow; storage at low state-of-charge causes this.

Supercapacitor: Electrochemical capacitor also known as an ultracapacitor or double-layer capacitor; specific energy is a fraction of Li-ion. Has high cycle life; offers good cold temperature performances.

System Management Bus (SMBus): Protocol for smart battery (See SMBus in Glossary).

Thermal runaway: Uncontrolled disintegration of a battery from the inside out; can be caused by cell defect, overcharging, excess heat and other abusive conditions.

Thermal voltage: A voltage created by the junction of dissimilar metals when a temperature difference exists between these junctions

Thermistor: Electrical resistor that changes resistance with temperature.

Titanate: Substance used for anode material of some lithium-based batteries.

Trickle charge:  Also known as maintenance charge, compensates self-discharge of a battery.

UL 1642: Safety acceptance test for lithium-based batteries by Underwriters Laboratories. Other agencies are IEC 62133, IEEE 1625, IEEE 1725, BAJ (Japan), UN. In 2010, UL 1642 transitioned to IEC 62133, made fully effective on 1 May 2012.

UN 38.3: Safety norms for shipping battery products

Universal Serial Bus (USB): Bi-directional data port featuring a 5-volt supply and two data lines to accommodate auxiliary devices and to charge batteries.

Valve-regulated lead acid (VRLA): Maintenance-free lead acid battery recombines oxygen (positive plate) with hydrogen (negative plate) on charge; valve regulates pressure by release of excess gases. Repeated venting will lead to dry out.

Vinylene carbonate: Additive to improve performance of Li-ion cathode. 

Voltage (V): Electric energy potential per unit charge. 1V = 1J/Coulomb. (1,000 joules = 0.277Wh).

Voltage delay: During prolonged storage, some battery systems develop a passivation layer. This results in a momentarily lower voltage until the film is dissipated through discharge.

Voltage limit: Battery thresholds on charge and discharge.

Voltage-limiting charger: Current is allowed to fluctuate in saturation mode while the voltage is capped (lead acid and Li ion charging).

Volumetric energy density: Also known as energy density; specifies energy storage in volume (Wh/l). (See Energy Density in this Glossary)

Watt (W):  Unit of power; ampere (A) times volt (V) equals watts (W).

Watt-hour (Wh): Unit of electrical energy equivalent to a power consumption of one watt for one hour (One watt-hour = 3600 Joules). Multiplying a battery voltage (V) by the rated capacity (Ah) gives the battery energy in Wh. Example: 14.4V x 2.5 Ah = 36 Wh.

Wi-Fi:  Wireless Internet connections; based on 2.4GHz 802.11b standard.

Zapping: Applying a momentary current pulse to a battery to evaporate a short.

Zinc-air: Generates electrical energy by an oxidation process of zinc and oxygen. Most zinc-air batteries are non-rechargeable, provide high specific energy but have poor load capabilities.

Last updated 2016-04-27


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