Battery Terminology: An Exhaustive Compilation of Terms, Definitions, and Glossary

Acid: A chemical substance capable of releasing hydrogen ions when mixed with water. Lead-acid batteries use sulfuric acid.

Active Material: The porous structure of lead compounds within a lead-acid battery that generates and stores electrical energy. The positive plates contain lead dioxide, while the negative plates consist of metallic sponge lead. During charging and discharging, these materials react with sulfuric acid following the chemical equation: PbO2 + Pb + 2H2SO4 = 2PbSO4 + 2H2O.

AGM (Absorbent Glass Mat): A non-woven separator material composed mainly of glass microfibers. It absorbs and retains the electrolyte, preventing spillage. VRLA batteries utilizing this material are commonly referred to as “AGM” batteries.

Ampere (Amp, A): The unit of measurement for the rate of electron flow, also known as current, in an electrical circuit.

Ampere-Hour (Amp-Hrs, Ah): A unit of measurement for a battery’s electrical storage capacity, obtained by multiplying the current in amperes by the duration in hours of discharge. For example, a battery delivering 5 amperes for 20 hours has a capacity of 5 amperes x 20 hours = 100 amp-hours.

Battery: A single or multiple galvanic (electrochemical) cells connected together, equipped with external electrical connections.

Battery Charger: A device that supplies electrical energy to recharge a battery.

Boost Charge: The process of adequately charging the cells and plates within a battery to enable proper functioning. Boost charging typically involves a brief period of high current.

BCI Group: The Battery Council International (BCI) Group Number serves as an identification for batteries, based on dimensions, voltage (6V or 12V), polarity, and terminal type. The BCI Group Number does not indicate battery capacity, only physical characteristics.

Capacity: The capacity of a battery refers to the number of amp-hours it can deliver at a specific discharge rate and temperature. It is not a constant value and tends to decrease as the discharge rate increases. Various factors, such as active material weight, plate design, electrolyte quantity, temperature, and more, influence battery capacity.

Cell: The fundamental electrochemical unit within a battery, comprising positive plates, negative plates, electrolyte, separators, and casing. In a lead-acid battery, each cell has an open-circuit voltage of approximately 2 volts. A 12-volt lead-acid battery consists of six cells.

Charge Acceptance: The amount of current, measured in ampere-hours, that a battery in a specific charge state can accept within a defined period, at a specified temperature and charge voltage.

Circuit: The path along which electrons flow in an electrical system. A closed circuit forms a complete path, while an open circuit has a broken or disconnected path.

Circuit (Parallel): A circuit that provides multiple paths for current flow. When batteries are connected in parallel, their positive terminals are connected to one conductor, and their negative terminals are connected to another conductor. For example, two 12-volt batteries of 50 ampere-hour capacity each connected in parallel would create a circuit with 12 volts and a combined capacity of 100 ampere-hours.

Circuit (Series): A circuit with a single path for current flow. Batteries connected in series have their negative terminal connected to the positive terminal of the next battery, creating a cumulative voltage. For instance, two 12-volt batteries of 50 ampere-hour capacity each connected in series would result in a circuit voltage of 24 volts and a combined capacity of 50 ampere-hours.

CCA: Cold Cranking Amps is a measure used in the battery industry to determine a battery’s capability to start an engine in cold temperatures. It represents the amount of current required to start the engine, but only for a short duration. The CCA rating indicates the number of amps that a fully charged battery can deliver at 0°F for 30 seconds while maintaining a voltage of at least 7.2 volts (for a 12-volt battery). As a battery ages, it may not meet its original CCA rating. A higher CCA rating indicates greater starting power of the battery.

Conductance: The ability of a circuit or battery to transmit electric current.

Container and Cover: The reservoir and lid that house the components and electrolyte of a battery. They are made from materials such as polypropylene, which are resistant to impact and acid.

Corrosion: The chemical or electrochemical reaction between a material, typically a metal, and its surrounding environment, leading to the deterioration of the material and its properties. Positive lead grids in a battery can gradually corrode, often resulting in battery failure. Battery terminals are also prone to corrosion if not properly maintained.

Current: The rate at which electricity flows or the movement of electrons along a conductor. It can be likened to the flow of a stream of water. The unit of measurement for current is the ampere.

Current (Alternating) (AC): An electric current that periodically varies in magnitude and direction. Batteries do not deliver alternating current.

Current (Direct) (DC): An electric current that flows in one direction only within an electrical circuit. Secondary batteries deliver direct current and must be recharged with direct current in the opposite direction of discharge.

Cycle: In a battery, one complete discharge followed by one recharge.

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Deep Discharge: A state in which a cell is fully discharged using low current, causing the voltage to fall below the final discharging voltage.

Deep-Cycle Battery: A battery designed to provide a steady amount of current over an extended period, capable of delivering surges when needed, and engineered to be deeply discharged repeatedly.

Discharging: The process in which a battery releases current to power a circuit or device.

Electrolyte: In a lead-acid battery, the electrolyte is a mixture of sulfuric acid diluted with water. It acts as a conductor, supplying water and sulfate for the electrochemical reaction: PbO2 + Pb + 2H2SO4 = 2PbSO4 + 2H2O.

Electronic Tester: An electronic device used to assess the condition of a battery by measuring its resistance or conductance, typically without drawing substantial current loads.

Element: A combination of positive and negative plates assembled with separators.

Equalization Charge: The process of ensuring that all cells and plates within a battery are fully charged, and the electrolyte is uniform and free from stratification. This is typically achieved by charging the battery under controlled conditions with specified charge current, time, and upper voltage limits.

Formation: In battery manufacturing, formation refers to the initial charging process of a battery. It chemically transforms 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: An electrolyte that has been immobilized by adding a chemical agent, usually fine silica, to prevent spillage. Batteries utilizing gelled electrolyte are often referred to as gel batteries, which are a common type of VRLA (Valve-Regulated Lead-Acid) battery.

Grid: A framework made of lead alloy that supports the active material of a battery plate and conducts electric current.

Ground: In a circuit, ground refers to the reference potential. In automotive applications, it involves connecting one battery cable to the body or frame of a vehicle, which serves as a pathway for completing a circuit instead of using a direct wire from a component. Nowadays, over 99 percent of automotive and LTV (Light Truck and Van) applications utilize the negative terminal of the battery as the ground.

Group Size: The Battery Council International (BCI) assigns numbers and letters to classify common battery types. These classifications adhere to standards regarding maximum container size, terminal type and location, and special container features.

Hydrometer: A device used to measure the strength, or concentration of sulfuric acid, in the electrolyte by determining its specific gravity.

Intercell Connectors: Lead structures that link adjacent cells in a battery in series, connecting the positive terminal of one cell to the negative terminal of the next.

Lead-Acid Battery: A battery composed of lead and lead oxide plates, along with various other elements that modify density, hardness, porosity, etc. The plates are immersed in a 35 percent sulfuric acid and 65 percent water solution called electrolyte, which triggers a chemical reaction producing electrons.

Load Tester: An instrument that draws current from a battery, discharging it through an electrical load, while simultaneously measuring voltage. It assesses the battery’s performance under actual discharge conditions.

Low Water-Loss Battery: A battery that does not require regular water addition under normal driving conditions. It is also referred to as a maintenance-free battery.

MCA (Marine): MCA is an industry rating that defines a marine battery’s capacity to deliver a high amount of amperage for a brief period. Since marine batteries are typically not used in freezing temperatures, marine cranking amps are measured at 32°F instead of 0°F like cold cranking amps. The MCA rating represents the number of amps that a marine battery can deliver at 32°F for 30 seconds while maintaining a voltage of at least 7.2 volts (for a 12-volt battery). A higher MCA rating indicates greater starting power for marine applications.

Maintenance-Free: A battery that typically does not require watering or other maintenance throughout its lifespan.

Negative: Pertaining to electrical potential, the negative battery terminal is the point from which electrons flow during discharge.

Ohm: A unit of measurement for electrical resistance or impedance within an electrical circuit.

Ohm’s Law: Ohm’s Law establishes the relationship between volts (V) and amperes (A) in an electrical circuit with resistance (R). It can be mathematically expressed as V = IR, where volts (V) equal amperes (I) multiplied by ohms (R). If any two of the three values are known, the third value can be calculated using this equation.

Open-Circuit Voltage: The voltage of a battery when it is not actively delivering or receiving power.

Plates: Thin, flat structures that consist of a grid and active material. The grid provides support to the active material and facilitates the flow of electrons out of the cell. Plates can be either positive or negative, depending on the type of active material they contain.

Positive: Referring to a type of electrical potential that is opposite to negative. It denotes a point or terminal on a battery with a higher relative electrical potential. During discharge, electrons flow toward the positive battery terminal.

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Primary Battery: A battery capable of storing and delivering electrical energy but unable to be recharged. It’s important to note that a lead-acid battery is not considered a primary battery.

Reserve Capacity Rating: The duration in minutes that a new, fully charged battery can deliver 25 amperes at a temperature of 27°C (80°F) while maintaining a terminal voltage equal to or higher than 1.75 volts per cell. This rating indicates how long the battery can power essential accessories in the event of an alternator or generator failure in a vehicle.

Resistance: The opposition encountered by current flow in a circuit or battery. It is commonly measured in ohms.

Sealed Battery: See VRLA (Valve-Regulated Lead-Acid).

Secondary Battery: A rechargeable battery capable of storing and delivering electrical energy. It can be recharged by passing direct current through it in the opposite direction of discharge. A lead-acid battery is an example of a secondary battery.

Separator: A porous divider positioned between the positive and negative plates within a cell. It allows the flow of ionic current while preventing the passage of electrical current. Separators are manufactured using various materials such as polyethylene, polyvinyl chloride, rubber, glass fiber, and cellulose.

Short Circuit: An unintended path that bypasses the normal current flow within an electrical device or wiring. In the context of batteries, a short circuit occurs when a conductive connection is formed between the positive and negative terminals. This can lead to the discharge of the cell and render the battery inoperable.

Specific Gravity (Sp. Gr. or SG): Specific gravity is a measurement of the electrolyte concentration in a battery. It is determined by comparing the density of the electrolyte to the density of water. Typically, a hydrometer (see Hydrometer) is used to measure specific gravity. Water has a specific gravity of 1.00, while the sulfuric acid electrolyte in a fully charged battery usually ranges from 1.265 to 1.285. Specific gravity measurements are often employed to assess the battery’s charge level or identify a faulty cell.

Splash Barrel: A splash barrel is a component of a battery’s vent system. Its purpose is to prevent acid from entering the vents when the battery is in an upright position. The splash barrel minimizes the splashing of acid within the cell caused by motion and vibration.

Starting, Lighting, Ignition (SLI) Battery: A rechargeable battery that provides electrical energy to an automobile, powering the starter motor, lights, and ignition system of the vehicle’s engine.

State of Charge (or State of Health): The level of deliverable low-rate electrical energy stored in a battery at a specific time, expressed as a percentage of the energy when fully charged and measured under the same discharge conditions. A state of charge of 100 percent indicates a fully charged battery.

Stratification: The uneven distribution of electrolyte within a cell due to density variations from the bottom to the top. This condition commonly occurs in batteries that are recharged from a deep discharge at a constant voltage without significant gassing. Continuous deep cycling of a stratified battery can cause deterioration in the lower portions of the positive plates. Equalization charging is a method used to prevent acid stratification.

Sulfation: The formation or conversion of lead sulfate in the battery plates into a state that hinders normal recharging. Sulfation often develops when a battery is stored or cycled in a partially discharged state at elevated temperatures.

Terminals: The electrical connections on a battery to which the external circuit is attached. Batteries typically have either top terminals (posts) or side terminals, while some batteries feature both types of terminals (dual terminal).

Vents: Mechanisms that allow gases to escape from the battery while retaining the electrolyte within the battery case. Flame-arresting vents often include porous disks that reduce the risk of internal explosions caused by external sparks. Vents can be permanently fixed or removable in design.

Volt: The unit of measurement for electrical potential or voltage.

Voltage Drop: The overall difference in electrical potential (voltage) measured across resistance or impedance (ohms). Its relationship to current is described by Ohm’s Law.

Voltmeter: An electronic device used to measure voltage, usually in a digital format.

VRLA: Valve-regulated lead-acid battery. VRLA batteries come in two types: Absorbent Glass Mat (AGM) and Gel batteries. These batteries do not have “free” liquid electrolyte and operate on the oxygen recombination cycle within the cell, minimizing water loss. VRLA batteries incorporate one-way burp valves in their vents, which prevent air from entering the cell while allowing gases to vent if necessary. The slight pressure maintained in the battery, typically below 3 psi, facilitates the conversion of oxygen generated at the positive plates back into water.

Watt: The unit of measurement for electrical power, representing the rate at which work is done in moving electrons by or against an electrical potential. It can be calculated using the formula: watts = amperes x volts.

Watt-Hour (Watt-Hrs, WH): The unit of measurement for electrical energy, expressed as the product of watts and hours.