Glossary of battery terms

Battery Terms

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Glossary of Battery Terms!

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The following summary is a short version of battery terms used in everyday dealings with batteries and battery technology. It is not comprehensive and is designed to provide the layman with a basic understanding of battery terms . It should enable the non-expert to understand the information provided by manufacturers and battery sellers to facilitate confidence in discussions with these organizations when making battery purchases.

A. All Battery Terms

  • AC
    Alternating current is the condition where the motion of electric charge in a conductor is periodically reversed.
  • Acid
    A chemical that can release hydrogen ions when mixed with water. Sulphuric acid, H2SO4, is used in a lead-acid battery as the electrolyte.
  • Accumulator
    A rechargeable battery or cell.
  • Active Material
    The chemicals in a battery that produce and store electrons within an electrochemical cell to be released as electrical energy. The active material reacts with the electrolyte on discharge to provide valence electrons from the oxidation and reduction reactions that occur at the positive and negative electrodes
  • AGM (Absorbent Glass Mat)
    This is a term often applied to a type of sealed recombinant lead-acid battery which uses a non-woven separator material composed almost entirely of glass micro-fibres that absorbs and retains the electrolyte between the plates in a cell. The AGM is actually the glass mat in the cell which is highly compressed to ensure that it absorbs the correct amount of acid and retains pressure on the active material to prevent loss of contact between the AM and the plate grids.
  • Ampere (Amp, A)
    The unit of measure of the electron flow rate through a circuit. 1 ampere = 1 coulomb per second.
  • Ampere-Hour (Amp-hrs, Ah): A unit of measure for a battery’s electrical storage capacity, obtained by multiplying the current in amperes by the time in hours of discharge. (Example: A battery that delivers 5 amperes for 20 hours delivers 5 amperes x 20 hours = 100 amp-hrs of capacity.)
  • Anode: The negative electrode of a cell. The anode loses electrons during discharge (oxidation) and gains electrons during charge (reduction).
  • Battery: One or more electrochemical cells electrically attached in series or parallel by intercell connections.
  • BMS: Electronic system that monitors a battery pack to maximise its life of and protect it from damage due to factors such as over and undercharging, individual cell imbalance and extreme temperature variations. The battery pack should also provide a safety function and allow communication with other devices.
  • Boost Charge: One or more additional short fast charges applied to a battery, normally during one service cycle, to ensure that it will complete its application duty.
  • BCI Group: The Battery Council International (BCI) Group Number identifies a battery by its physical and electrical characteristics. The dimensions (L x W x H), voltage, terminal layout polarity, and the terminal shape and type. This characterisation enables the buyer to identify a battery that will fit their vehicle.
  • Capacity: The capacity of a battery is specified as the number of amp-hrs that the battery will deliver at a specific discharge rate and temperature. The capacity of a battery is not a constant value and is seen to decrease with increasing discharge rate. The capacity of a battery is affected by a number of factors such as active material weight, density of the active material, adhesion of the active material to the grid, number, design and dimensions of plates, plate spacing, design of separators, specific gravity and quantity of available electrolyte, grid alloys, final limiting voltage, discharge rate, temperature, internal and external resistance, age and life history of the battery.
  • Cathode: The positive electrode of a cell. The cathode gains electrons during discharge (reduction) and loses electrons during charge (oxidation).
  • Cell: An abbreviation of an electrochemical cell. This consists of two dissimilar materials, usually metals within an ionic conducting electrolyte. The dissimilar metals provide a potential difference based on their position in the electrochemical table. This difference produces an EMF or single-cell voltage which defines the voltage of batteries. For Nickel Cadmium this is 1.2 V per cell and for lead-acid, it is 2 volts.
  • Charge Acceptance: A battery’s ability to accept and store energy under given external parameters like time, temperature, state-of-charge, charging voltage or battery history. It is generally linked to the batteries internal resistance and capacity.
  • Cold Cranking Amps (CCA): This is a rating given to 12V Starter Lighting Ignition (SLI) batteries to show their ability to start an engine in cold weather. It is defined as the number of amps that can be removed from a new fully charged battery at -180C for 30 seconds while maintaining a voltage greater than 7.2 volts.
  • Charger: A device to supply electrical energy to a battery when it is in a discharged condition.
  • Conductance: The ease with which electric current flows through a substance. In equations, conductance is symbolized by the uppercase letter G. The standard unit of conductance is the siemens (abbreviated S), formerly known as the mho which is the reciprocal of resistance (ohm)
  • Container: The box which holds the cell or battery components. It has to be inert to the electrolyte used and as impact resistant as possible.
  • Corrosion: The chemical or electrochemical reaction of a material and its environment in which the material usually a metal produces a compound as a product of the reaction. In metals, it is brought about by the oxidation (electron loss) reaction which results in a metal compound e.g. Pb discharging to PbSO4 in the presence of sulphuric acid.
  • Current: Any movement of electric charge carriers, such as subatomic charged particles (e.g., electrons having a negative charge, protons having positive charge), ions (atoms that have lost or gained one or more electrons), or holes (electron deficiencies that may be thought of as positive particles). The electric current in a wire, where the charge carriers are electrons, is a measure of the quantity of charge passing any point of the wire per unit of time.
  • Cycle: In battery terms, one cycle is a complete sequence of one discharge from a fully charged condition plus one complete recharge to a fully charged condition.
  • Cycle life: The number of defined charge-discharge cycles that a battery can complete until its voltage on discharge reaches a minimum set value. the parameters of the depth of discharge, rate of discharge and recharge, voltage settings for charge and discharge plus the temperature are normally defined to describe the nature of a cycle life test. The number of cycles that a battery will complete is dependent on many factors in addition to the set test parameters. Typical factors are the design of the batteries, their chemistry and the constructional materials.


  • Deep Discharge: This is a discharge using a current which puts a battery into a state where the voltage is the minimum recommended by the manufacturer for a particular discharge rate. For example, a lead-acid traction battery would be discharged to 1.7 volts per cell over a 5 hour period would be 100% discharged at a rate of C5.
  • Deep-Cycle Battery: A battery that is designed to give the maximum number of cycles when discharged to the manufacturer’s minimum recommended voltage for a particular discharge rate.
  • Discharging: When a battery is connected to a load and provides a current, it is said to be discharging.

E. Even more Battery terms!

  • Electrolyte: An electrochemical battery requires a conducting medium for the transfer of ions to enable the charging and discharging of the positive and negative electrodes.
    In a lead-acid battery, the electrolyte is sulfuric acid diluted with water. It is a conductor that supplies water and sulphate for the electrochemical reaction:
    PbO2 + Pb + 2H2SO4 = 2PbSO4 + 2H2O.
    In a Lithium-ion battery the electrolyte does not react with the electrodes it simply transfers Li+ ions from the cathode to the anode when charging and from the anode the cathode on discharge
  • Electronic Tester: An electronic device that assesses the condition of a battery through a resistive or impedance measurement which can include ohmic resistance, capacitance, metallic and ionic conductance. Often these devices will use high-frequency pulses and draw low currents.
  • Element: A set of positive and negative plates assembled with separators between the plates.
  • Equalization Charge: The process of ensuring that all of the cells within a battery are in a fully charged state. The electrolyte of each cell should also be of uniform density and free of stratification. This is normally a process carried out in multiple battery connected installations were undercharging or frequent discharging prevents individual batteries or cells from reaching the same state of charge. The charge current is usually low and the time period can be up to several days.
  • Formation: In battery manufacturing, formation is the process of charging the battery for the first time. Electrochemically, formation changes the lead oxide paste on the positive grids into lead dioxide and the lead oxide paste on the negative grids into metallic sponge lead.
  • GEL: The name often applied to the electrolyte of a lead-acid battery that has been mixed with a chemical agent to produce an immobilised non-liquid structure. This can be done by using a polymerising agent or by the addition of fine silica powder. The purpose is to prevent spillage of the electrolyte and to enable recombination of hydrogen and oxygen which are leased by the breakdown of water on charging (see VRLA batteries). Batteries made with a gelled electrolyte are often referred to as GEL batteries.
  • Grid: A metal or metal alloy framework that supports the active material of a battery plate. It conducts current produced by the active material to the battery terminals when discharging and from the terminals to the active material on a charge.
  • Ground: The reference potential of a circuit. In automotive use, the result of attaching one battery cable to the body or frame of a vehicle that is used as a path for completing a circuit in lieu of a direct wire from a component. Today, over 99 per cent of automotive and LTV applications use the negative terminal of the battery as the ground.
  • Group: A single cell from a battery comprised of the correct number of positive and negative plates with separators that will achieve the rated capacity of the battery.

  • Group Size: The Battery Council International (BCI) assigns numbers and letters for common battery types. There are standards for maximum container size, location and type of terminal and special container features.

  • Hydrometer: A device used to estimate the concentration of acid or alkaline in battery electrolyte by measuring its specific gravity.
    Intercell Connectors: Structures that connect adjoining cells in series, positive of one cell to the negative of the next, within a battery.

  • Impedance (Z): The effective resistance of an electric circuit or component to alternating current. It arises from the combined effects of ohmic resistance and reactance and has the same unit as resistance i.e. ohms.


  • Internal resistance (IR): A battery has resistance, capacitance and inductance. Given below is a representation of a battery total resistance which is called the Randles model

    Ro= Ohmic resistance of Battery metallics + Electrolyte + Separators
    RCT= Charge transfer resistance across the electrical double layer (EDL)
    Cdl=Capacitance of the double layer
    L=High frequency inductance of the metallic components
    Zw= Warburg impedance representing mass transport effects
    E=EMF of the circuit

Battery internal resistance
  • Lead-Acid Battery: Battery made up of plates comprising a lead alloy conductor and lead oxide active material for the positive and pure spongy lead for the negative. The electrolyte is dilute sulphuric acid in the range of 30 to 40% by weight of acid.
  • Load Tester: An instrument that draws current from a battery while measuring voltage. It determines the battery’s ability to provide capacity
  • Low Maintenance battery: A battery that does not require frequent water additions to top up the electrolyte. Generally 3 to 6 months between additions with controlled charging.

M. More Battery terms!

  • MCA (Marine cranking amps): MCA is an industry rating defining a marine battery’s ability to deliver a large amount of amperage for a short period of time. Since marine batteries are typically never used at temperatures below freezing, marine cranking amps are measured at 32°F (0°C) as opposed to 0°F (-18C) for cold-cranking amps. The rating is the number of amps that can be removed from a marine battery at 32°F for 30 seconds while maintaining a voltage of at least 7.2 volts for a 12-volt battery. The higher the MCA rating, the greater the starting power of the marine battery.
  • Maintenance-Free: A battery that normally requires no service watering during its lifetime of use when using correct charging methods.
  • Negative: The direction of electron flow which describes electrical potential. The negative battery terminal provides electrons to reduce the plate active material during charge.
    Mx+ + xe = M
  • Ohm (Ω): A unit for measuring electrical resistance or impedance within an electrical circuit. Defined in SI units as the SI unit of electrical resistance, transmitting a current of one ampere when subjected to a potential difference of one volt.
  • Ohm’s Law: The relationship between current, voltage and resistance for a conductor in an electrical circuit
    V = IxR (where V = volts, I = amps and R = ohms)
  • Open-Circuit Voltage: The voltage of a battery when the terminals are in open circuit, i.e. not under load
  • Plates: These are the electroactive components of a battery forming the positive and negative electrodes. They consist of a rigid conductor which supports the active material. The conductor can be in more than one form, e.g. a strip or sheet supporting active material or a grid structure which improves the conductor/active material adherence and reduces overall battery weight. Plates are either positive or negative, depending on the polarity of the battery’s electrodes for which they are used.
  • Positive: The point from which current flows to the negative part of a circuit in conventional physics. The point or terminal on a battery having higher relative electrical potential. In a battery, the positive plate provides an oxidation reaction by depleting electrons from the active material which flow to the negative plate to make a reducing reaction.
  • Primary Battery: A battery that can store and deliver electrical energy but cannot be electrically recharged. Typical chemistries include: (i) carbon-zinc (Leclanche cells), (ii) alkaline-MnO2, (iii) lithium-MnO2, (iv) lithium-sulphur dioxide, (v) lithium-iron disulphide, (vi) lithium-thionyl chloride (LiSOCl2), (vii) silver-oxide, and (viii) zinc-air
Traditional current and electron direction


  • Reserve Capacity Rating: The time in minutes that a new fully charged SLI battery will deliver 25 amperes at 27°C (80°F) and maintain a terminal voltage equal to, or higher than, 1.75 volts per cell. This rating represents the time the battery will continue to operate essential accessories if the alternator or generator of a vehicle fails.
  • Resistance (Ω): Electrical resistance is the opposition to the free flow of current in a circuit or battery. Resistance converts electrical energy to thermal energy, and in this regard is similar to mechanical friction. When a voltage is applied to a metal in a circuit, it causes a net movement of electrons in the metal’s conduction band.
  • The movement of electrons is hindered by the vibration of the atoms in the metal lattice, which causes part of the electrical energy of the electric current to be lost as heat, this is resistance. Since lattice vibrations increase as the temperature rises, the resistance of metals also increases as the temperature rises. In a battery, resistance is partly metallic due to the conductors, partly ionic due to the electrolyte and separators and partly inductive due probably to the creation of a magnetic field by the metallic conductors in the battery.

S. Still more battery terms!!

  • Sealed Battery: Most recombination batteries are sealed with a pressure relief valve to prevent gas escape and facilitate oxygen and hydrogen to recombine to form water (see VRLA). There are also batteries which are no maintenance and sealed to prevent internal access, but with vents not under pressure to allow gas to escape freely. These are very low water loss batteries that are not recombinant but will last for their warrantied lifetime of several years.
  • Secondary Battery: A battery that can store and deliver electrical energy and can be recharged by passing a direct current through it in a direction opposite to that of discharge.
  • Separator: A porous divider between the positive and negative plates in a cell that allows the flow of ionic current to pass through it. Separators are made from numerous materials such as polythene, PVC, rubber, glass fibre, cellulose and a variety of polymers for different electrochemistry.
  • Short Circuit: A direct low resistance connection between the positive and negative source of an electrical power supply. In a battery, a short circuit can be externally caused between the two terminals, internally a cell short circuit can be the result of contact between the positive and negative plates caused by faulty separators or bridging of the plates by loose active material or even a manufacturing fault.
  • Specific Gravity (Sp. Gr. or SG): Specific gravity is a measure of the electrolyte concentration in a battery. This measurement is based on the density of the electrolyte compared to the density of water and is typically determined by the use of a float or an optical hydrometer
  • Starting, Lighting, Ignition (SLI) Battery: This is a rechargeable battery that supplies electric energy to an automobile to power the starter motor, the lights and the ignition system of a vehicle’s engine. Almost invariably a lead acid battery
  • State of Charge (or the State of Health): The amount of deliverable low-rate electrical energy stored in a battery at a given time expressed as a percentage of the energy when fully charged and measured under the same discharge conditions. If the battery is fully charged, the state of charge is said to be 100 per cent.
  • Stratification: The unequal concentration of electrolyte due to density gradients from the bottom to the top of a cell. Often found in lead-acid batteries recharged from a deep discharge at a constant voltage. It is the result of high-density acid being formed at the plate surface which immediately sinks to the bottom of the cell due to the low density of the discharged battery electrolyte. Unless the electrolyte is stirred by occasionally gassing at a higher charge voltage, stratification can seriously reduce the life of a lead-acid battery by damaging the active material.
  • Sulfation: A condition or process in lead-acid batteries caused by leaving the battery in a discharged or low state of charge condition for long periods. The discharge reaction produces lead sulphate in both positive and negative plates and in the case of some lead-acid batteries, particularly those with lead calcium grids it can lead to passivation of the grids with high resistance. This can in severe cases prevent normal recharge of the battery rendering it virtually useless.
  • Terminals: The external electrical conductors on the battery to which an external circuit is connected. Typically, batteries have either top terminals (posts) or side (front) terminals. Some batteries have both types of terminals (dual terminal).
  • Vents: Devices that allow gases to escape from the battery while retaining the electrolyte within the case. Flame-arresting vents typically contain porous disks that reduce the probability of an internal explosion as a result of an external spark. Vents come in both permanently fixed and removable designs. For VRLA batteries the vents contain a pressure relief valve
  • Volt (V): The SI unit of electromotive force, the difference of potential that would carry 1 ampere of current against 1-ohm resistance.
  • Voltage Drop: The net difference in the electrical potential i.e. voltage when measured across a resistance or impedance. Its relationship to current is described in Ohm’s law.
  • Voltmeter: An electronic device used to measure voltage, either in a digital or analogue format.
  • VRLA: This a description of lead-acid batteries which have one-way pressure relief valves which prohibit air ingress to the cell but allow gases produced on charge to escape if the internal cell pressure is too high. Typically between 0.1 and 0.3 psi, the pressure is required to ensure the oxygen and hydrogen produced on charge are able to recombine to water in the cell. AGM and gel are the two types of VRLA batteries. These batteries have an immobilised liquid electrolyte, this is achieved by either using a glass mat (AGM) or a gelling agent (GEL).
  • Watt (W): the SI unit of power, equivalent to one joule per second, corresponding to the rate of consumption of energy in an electric circuit where the potential difference is one volt and the current one ampere.
  • watt = 1 Amp x 1 Volt
  • Watt-hour (Wh)
    The unit of measure for electrical energy expressed as watts x hours. It is the energy that a battery produces not the capacity which is measured in ampere-hours.
    1 watt hour = 1 Amp x 1 Volt x 1 hour

Okay, we have exhausted our battery terms! Please feel free to add your battery terms you have come across, so we can add it here! Thanks in advance

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