A
AGM (Absorbed Glass Mat): A separator material made almost entirely of very fine glass fibers that absorbs and holds the electrolyte, leaving no free liquid inside the cell that could leak or spill. VRLA batteries that use this separator are commonly known as AGM batteries.
Active Materials: The substances inside a battery that undergo chemical reactions to generate electrical energy. In a lead-acid battery, the active materials are lead dioxide on the positive plate and sponge lead on the negative plate.
Alternating Current: An electric current that periodically changes direction, causing a terminal to become positive and negative in rapid succession.
Ammeter: An instrument used to measure electric current. See also Ampere-Hour Meter.
Ampacity: The maximum current, expressed in amperes, that a conductor or circuit can safely carry.
Ampere: The practical unit of electric current, equal to the steady current produced when one volt is applied across a resistance of one ohm. It is one-tenth of an abampere.
Ampere-Hour: A unit used to measure the quantity of electricity, equal to one ampere flowing for one hour, or 3,600 coulombs. It is commonly used to indicate battery capacity and is determined either by an ampere-hour meter or by multiplying the current in amperes by the time during which it flows.
Ampere-Hour Capacity: The amount of ampere-hours a battery can deliver under specified conditions of temperature, discharge rate, and final voltage.
Ampere-Hour Efficiency: The electrochemical efficiency of a battery, expressed as the ratio of the ampere-hours delivered during discharge to the ampere-hours required for recharge.
Ampere-Hour Meter: An instrument that records the quantity of electricity transferred, expressed in ampere-hours.
B
Bayonet Vent: Used to describe a quarter-turn vent plug whose lower section resembles a bayonet in both shape and locking mechanism.
Boost Cells: Cells with a higher capacity than the test cells, used during a manual discharge test to help keep the discharge current constant.
Boost Charge: A supplementary or partial charge applied to a storage battery, typically at a relatively high charging rate for a short time. It is commonly used in motive-power applications when the battery does not have enough capacity to complete a full day of operation.
Boot: A plastic component attached to the bottom of a plate, particularly a wrapped plate, to provide retention and electrical insulation.
Bridge: A ribbed or supporting structure that is molded or cut to fit into the bottom of a ribless jar or container. Its purpose is to create sediment space beneath the element and thereby reduce the possibility of short circuits.
Burning: The process of joining two or more lead components—such as plates, straps, or connectors—by applying heat and, in some cases, adding extra lead supplied from a rod known as a burning strip.
Burning Center: The center-to-center spacing between neighboring plates of the same polarity.
Burning Stick: A lead rod of convenient dimensions used as a source of filler metal during the lead-burning process.
C
Capacity Test: A test in which a battery is discharged at a constant current at room temperature until it reaches a specified cutoff voltage, typically 1.70 volts per cell.
Carbon Burning Outfit: A tool consisting of a metal rod with an insulated handle that holds a pointed carbon rod, used for lead-burning work in field or service locations where standard gas-flame equipment is unavailable.
Casting: A metal component, such as a grid, strap, or connector, formed by introducing molten metal into a mold and letting it harden.
Cell (Storage): A secondary or storage cell is an electrolytic cell that generates electrical energy and can be restored to a charged condition after discharge by applying an electric current in the reverse direction of the discharge current.
Charged: The state of a storage cell when it is capable of delivering its maximum current. The positive plates contain the maximum amount of lead peroxide and minimum sulfate, the negative plates contain the maximum sponge lead and minimum sulfate, and the electrolyte has its highest specific gravity.
Charged and Dry: A battery assembled with dry, charged plates but without electrolyte.
Charged and Wet: A fully charged battery containing electrolyte and ready for use.
Charging Plug: The male portion of a quick connector that contains both the positive and negative conductors.
Circuit: A system of electrical components that provides a continuous path through which electric current is intended to flow.
Circuit (Series): A circuit with only one current path. Batteries connected in series have the negative terminal of one battery connected to the positive terminal of the next. In a series connection of two 12-volt batteries rated at 50 ampere-hours each, the total voltage becomes 24 volts while the capacity remains 50 ampere-hours.
Circuit (Parallel): A circuit that offers multiple paths for current flow. In a parallel connection, all positive terminals are connected together and all negative terminals are connected together. Two 12-volt batteries rated at 50 ampere-hours each connected in parallel provide 12 volts and a combined capacity of 100 ampere-hours.
Cold Crank Rating: The number of amperes a lead-acid battery can deliver at 0°F (-17.8°C) for 30 seconds while maintaining at least 7.2 volts (1.2 volts per cell). This value is commonly known as CCA (Cold Cranking Amps).
Corrosion: A chemical or electrochemical reaction between a material, usually a metal, and its environment that causes deterioration of the material and its properties. In batteries, positive lead grids gradually corrode during service, which can eventually lead to failure, and terminals may also corrode if not properly maintained.
Constant-Current Charge: A charging method in which the charging current is kept constant throughout the process. Some lead-acid batteries may use two current levels, referred to as the starting rate and the finishing rate.
Constant Voltage Charge: A charging method in which the battery terminal voltage is maintained at a constant value.
Cover Inserts: Lead or lead-alloy rings molded or sealed into the cell cover, to which the element posts are burned, creating an effective seal that resists acid creep.
Curing: A chemical conversion process in which lead oxides and sulfuric acid are transformed into tetrabasic lead sulfate and other basic lead compounds that later develop into the desired Pb or PbO2 structures on the negative and positive plates during formation.
Cutting (of Acid): The process of diluting a concentrated sulfuric acid solution to a lower concentration.
Cycle Service: A mode of battery operation in which the battery is repeatedly subjected to successive charge and discharge cycles, such as in motive-power applications.
D
Deep Discharge: Removal of up to 80% of the rated capacity of a cell or battery.
Direct Current (DC): A direct current is a unidirectional current in which the changes in value are either zero or so small that they may be neglected.
Discharged: The condition of a storage cell when as the result of delivering current, the plates are sulfated, the electrolyte is exhausted, and there is little or no potential difference between the terminals.
Discharge Rate: Batteries discharged to meet any time rate between 3 hours and 8 hours are considered as having been normally discharged.
Dry Charging: Manufacturing process whereby charged plates are washed free of acid and then dried.
E
Electrolysis: An electrochemical process that causes a compound, whether liquid, molten, or dissolved in solution, to break down into its constituent substances.
Electrolyte: Any substance that separates into two or more ions when dissolved in water. Electrolyte solutions are capable of conducting electricity and are chemically decomposed by the passage of electric current. In battery terminology, electrolyte generally refers to a diluted sulfuric acid solution.
Electronic Tester: An electronic instrument used to evaluate the condition or health of a battery by performing an ohmic measurement, such as resistance or conductance, usually without applying high current loads.
Electromotive Force (EMF): The electrical pressure or potential of a circuit or battery, measured in volts.
Equalizing Charge: A prolonged charging operation applied to a storage battery to ensure that the active materials in all plates of every cell are fully restored and balanced.
F
Ferroresonant Charger: A constant-voltage power supply that uses a specially designed transformer and capacitor combination. As the current demand changes, the operating characteristics of this combination adjust to maintain a consistent output voltage.
Final Voltage: The specified cutoff voltage of a battery, indicating that the discharge process has reached its prescribed endpoint.
Finishing Rate: The charging current, expressed in amperes, to which the charging rate is reduced near the end of the charging process in certain lead-acid batteries. This lower rate helps prevent excessive gassing and excessive temperature increase.
Fixed Resistance Discharge: A discharge method in which a cell or battery is connected to a fixed-resistance load. As the battery terminal voltage decreases, the discharge current is allowed to decrease accordingly.
Flat Plate: A general term used to describe pasted battery plates.
Float Charging: A method of maintaining a battery at full charge by continuously applying a very low charging current through a bus whose voltage is slightly higher than the battery's open-circuit voltage.
Flush: The process of adding water to a battery cell.
Flying Leads: A fixed terminal cable in which the terminal or connector at the end is not mechanically supported and is allowed to hang freely along the side of the battery.
Foot: A portion of the battery grid that extends downward from its bottom edge and provides support for the plate group.
Formation or Forming Charge: The initial charging process during which the raw paste in the battery plates is electrochemically transformed into active charged material. Lead peroxide is produced in the positive plates, while sponge lead is formed in the negative plates.
Freshening Charge: A periodic charge applied to batteries kept in storage to compensate for charge lost through standing loss and to ensure that all plates in every cell are regularly returned to a fully charged condition.
Full Charge Gravity: The specific gravity of the electrolyte measured when the battery cells are fully charged and the electrolyte level has been properly adjusted.
G
Gang Vent: A venting arrangement in which the vents of typically three neighboring cells are connected to a shared manifold. This configuration is commonly used in SLI (Starting, Lighting, and Ignition) batteries.
Gassing: The release of gases from one or more electrodes as a result of the electrolysis process.
Gelled Electrolyte: An electrolyte that has been immobilized through the addition of silica powder or another substance that forms a gel.
Gravity Drop: The decrease in the specific gravity of the electrolyte, expressed in points, that occurs when a cell is discharged.
Ground: The reference electrical potential of a circuit. In automotive applications, it is commonly established by connecting one battery cable to the vehicle body or frame, which serves as the return path for current instead of using a separate wire. In more than 99% of modern automotive and light-truck applications, the battery’s negative terminal is used as the ground connection.
Group: One or more plates of the same polarity (positive or negative) that are joined to a common strap and post by lead-burning.
H
High Rate: During charging, any charging current that exceeds the normal finishing rate.
H₂SO₄: The chemical formula for sulfuric acid.
Hydrometer: An instrument used to measure the density or specific gravity of electrolyte solutions.
Hydroset: A curing process applied to positive and negative plates in which the free lead present in the paste is oxidized, reducing the total amount of free lead to only a small percentage.
I
Initial Voltage: The closed-circuit voltage measured at the start of a discharge. It is generally taken after the discharge current has been flowing long enough for the voltage change to become essentially stable.
Insert: A lead or lead-alloy bushing that is molded or sealed into the cell cover to form the post opening, and to which the post is lead-burned in order to create a seal resistant to acid creep.
Intercell Connector: A conductor made of lead, lead alloy, or lead-plated copper used to electrically connect two battery cells.
Internal Resistance: The resistance inside a cell or battery that opposes the flow of electric current. It is determined by the ratio of the change in terminal voltage to a specified change in current over a short time interval.
J
Jar Cell: A cell container manufactured by processes such as injection molding, rotational molding, or thermoforming.
Jar Formation: The process of forming the battery plates after they have been assembled inside the cell jar or container.
Jumper: A short conductor used to connect, bypass, or isolate a portion of an electrical circuit.
K
Kilovolt (KV): One thousand volts.
Kilowatt (KW): One thousand watts.
Kilowatt Hours (KWH): A measure of energy or work accomplished, being 1000 watt hours.
L
Lamp Black: A very fine carbon powder used as a component of the expander material in negative battery plates.
Lead (Pb): The chemical element lead, used together with sulfuric acid and other materials in lead-acid batteries.
Lead Hydrate: A white lead compound of variable composition produced when metallic lead or lead alloys react with water or very dilute electrolyte.
Lead Oxide: A collective term for the finely divided lead oxides used in preparing battery paste for storage batteries.
Lead Peroxide: A brown lead oxide that serves as the active material of a fully formed positive plate; chemical formula PbO₂.
Lead-Plated Part: A metal component coated with a thin protective layer of metallic lead deposited on its surface.
Lead Sponge (Pb): The principal constituent of the active material in a fully charged negative plate.
Lead Sulfate (PbSO₄): A compound formed when sulfuric acid reacts with lead oxides or with metallic lead.
Lifting Ear: An extension on the side of a battery tray containing a hole or slot that allows the battery to be lifted or handled.
Litharge (PbO): A yellowish-red lead monoxide that may be used in the preparation of battery active material.
Loss of Charge: The reduction in battery or cell capacity that occurs while it remains on open circuit due to local action.
Low Water Loss Battery: A battery designed to require little or no addition of water during normal operation; also known as a maintenance-accessible battery.
Lug: The portion of a grid used to support the plate group, commonly located along the upper edge of the grid as a hanging lug. The term also refers to the tab used to connect the plate to the strap and to other plates.
M
Manual Discharge: A capacity test in which the operator manually connects and disconnects both the battery and the test load. The test is terminated after all cells have reached the specified final voltage. When fixed-resistance loads are used, boost cells help maintain a nearly constant discharge current as the voltage of the test cells falls rapidly near the end of discharge. Electronic load tests usually do not require boost cells.
Microporous Separator: A veneer-type or grooved separator made from a material containing a large number of extremely small pores.
Mine Locomotive Battery: A deep-cycle battery specifically designed for use in mine locomotives, trammers, shuttle cars, and other underground haulage equipment.
Millivolt (mV): One-thousandth of a volt.
Moss: Branch-like lead crystals that may develop in regions of high current density on negative plates, such as along edges, feet, or lugs, and that can eventually create an internal short circuit within the cell.
Moss Shield: A perforated plastic or hard-rubber sheet used to electrically insulate the spaces between negative plates and the positive strap, and between positive plates and the negative strap.
O
Ohm: Standard unit used to measure electrical resistance.
Ohm’s Law: Describes the relationship among voltage (V), current (I), and resistance (R) in an electrical circuit. The relationship is expressed by the equation V = I × R, meaning that voltage equals current multiplied by resistance. Knowing any two of these quantities allows the third to be calculated.
Open Circuit: The condition of a battery when it is disconnected from both a charging source and any external load.
Open Circuit Voltage: The voltage measured at the battery terminals when essentially no current is flowing.
Oxide (of Lead): Any of several compounds formed by the combination of lead and oxygen, such as gray oxide, litharge, red lead, or lead peroxide, which are used in the preparation of battery paste.
P
Panel: A casting made up of two or more grids produced at the same time within a single mold.
Pb: The chemical symbol for lead.
PbO: The chemical symbol for litharge, or lead monoxide.
PbO₂: The chemical symbol for lead peroxide (lead dioxide).
Pellet: The portion of pasted material contained within a section of the grid bounded by adjacent horizontal and vertical grid members, excluding the forming bars.
Perforated Retainer: A thin, perforated plastic sheet positioned over each surface of a positive plate to help prevent the loss of active material. It is normally used together with one or more layers of insulating glass material.
Pig: A cast piece or bar of lead or lead alloy.
Pig Lead: A highly refined grade of lead containing no intentional alloying elements.
Pilot Cell: A designated cell within a storage battery whose temperature, voltage, and specific gravity are monitored and considered representative of the condition of the entire battery.
Plate: A battery grid covered with paste, whether it has undergone the formation process or not.
Plate Centers: The distance between the center lines of two adjacent plates having opposite polarities within a cell. This distance is therefore one-half of the strap-center dimension on which plates of the same polarity are attached.
Polarity: An electrical characteristic that establishes the direction in which current tends to flow. In conventional terminology, during discharge, current is considered to flow from the positive electrode through the external circuit toward the negative terminal.
Polarization: The change in terminal voltage that occurs when a specified current is flowing through a cell or battery. It represents the difference between the actual plate potential and the equilibrium potential, or constant open-circuit potential, excluding the voltage drop caused by internal resistance (IR drop).
Porosity: The proportion of empty spaces or voids within a material relative to its total volume.
Positive Plates: Battery plates consisting of a grid and active material from which current is delivered to the external circuit while the battery is discharging.
Positive Terminal: The terminal from which conventional current flows through the external circuit toward the negative terminal during battery discharge.
Post: A terminal or other conductive component that connects the plate-group strap to the exterior of the battery cell.
Post Builder: A ring-shaped mold used to rebuild or repair damaged battery posts.
R
Rated Capacity: The number of ampere-hours that can be delivered by a fully charged secondary cell or battery when discharged at a specified constant rate, temperature, and cutoff voltage.
Raw Plate: A battery plate that has not yet undergone the formation process.
Red Lead (Pb₃O₄): A red lead oxide used in the preparation of battery active material.
Reserve Capacity Rating: The number of minutes a new, fully charged battery can supply 25 amperes at 27°C (80°F) while maintaining a terminal voltage of at least 1.75 volts per cell. This rating indicates how long the battery can continue powering essential vehicle electrical accessories if the alternator or generator stops operating.
Resistance: The opposition presented by a conductor to the flow of electric current, normally measured in ohms.
Resistor: An electrical component designed to add a specific amount of resistance to a circuit.
Retainer: A sheet made of glass mat, perforated or slotted rubber, plastic, or another suitable material, positioned against each face of the positive plates in certain battery designs to help prevent the loss of active material.
Rib: A vertical or nearly vertical raised section of a grooved separator or spacer.
S
Sealing Compound: An asphalt-based material available in various formulations, each with different levels of heat resistance, adhesion, and resistance to shear. It is used to seal cell covers to battery jars or containers. See also Compound.
Secondary Lead: Lead recovered or reclaimed from previously used materials, as opposed to newly produced or virgin lead.
Sediment: Lead-containing sludge or active material that separates from the plates and accumulates at the bottom of the battery cells.
Sediment Space: The area at the bottom of a battery jar or container compartment located beneath the element, designed to collect a certain amount of material shed from the plates without causing an internal short circuit.
Self-Discharge: The loss of stored charge caused by local electrochemical action within the battery.
Shedding: The loss or separation of active material from the battery plates.
Short Circuit: An unintended low-resistance path that bypasses the normal current path in an electrical device or wiring. Outside a battery, a short circuit occurs when a conductive connection is made between its two terminals. Inside a battery, a cell short circuit occurs when the positive and negative plates come into contact, causing the cell to discharge and potentially making the battery unusable.
Sliver / Slyver: Extremely fine, parallel glass fibers placed next to the positive plate within retainers to help reduce the shedding of active material.
Specific Gravity (Sp. Gr. or SG): A measurement of electrolyte concentration based on the density of the electrolyte compared with the density of water. It is commonly measured with a hydrometer. Water has a specific gravity of 1.00, while the sulfuric acid electrolyte in a typical fully charged battery generally has a specific gravity between 1.265 and 1.285. Specific gravity readings are commonly used to determine whether a battery is fully charged and to identify a potentially defective cell.
Sponge Lead (Pb): The primary active material in a fully charged negative plate, consisting of a porous structure made up of lead crystals.
Stacking Fixture or Stacking Jig: A fixture or tool used to correctly position, stack, and burn the elements during cell assembly.
Standing Loss: The loss of charge experienced by an idle cell or battery as a result of local electrochemical action.
Starting Rate: The charging current, expressed in amperes, at which charging can initially begin without causing excessive gassing or bubbling of the electrolyte or raising the cell temperature above 110°F (43°C).
State of Charge: The amount of electrochemical energy remaining available in a cell or battery.
Stationary Battery: A storage battery intended to remain permanently installed in a fixed location rather than being regularly moved during operation.
Strap: A precast or cast-on lead or lead-alloy component used to join plates into groups and connect those groups to the battery post.
Stratification: The separation of electrolyte into layers, with higher-specific-gravity acid accumulating in the lower part of the cell where it does not readily mix with the rest of the electrolyte and therefore provides limited benefit.
Sulfated: A term describing a plate or cell whose active materials contain a significant quantity of lead sulfate.
Sulfation: The development or accumulation of lead sulfate on a plate or within a cell as a result of discharge, self-discharge, or pickling.
Sulfuric Acid (H₂SO₄): The principal acid compound of sulfur. When highly purified and diluted to the appropriate concentration, sulfuric acid serves as the electrolyte in lead-acid storage cells.
T
Temperature Correction: In storage batteries, specific gravity and charging voltage decrease as temperature increases, whereas open-circuit voltage increases slightly with rising temperature.
Tinning: The operation of applying a thin coating of molten tin or tin alloy to a metal surface.
Tray: A steel enclosure used to contain motive-power battery cells.
Treeing: The formation and growth of a lead filament or dendrite through an opening, crack, or large pore in a separator, eventually creating an internal short circuit within the cell.
Trickle Charge: A continuous low-rate charge applied to a storage battery at approximately the same level as its internal losses, intended to keep the battery in a fully charged condition.
Tubular Plate: A positive battery plate consisting of a cast lead-alloy spine surrounded by porous tubes that are filled with paste or dry oxide material.
TVR: A temperature-compensating voltage relay used in battery charging equipment.
Two-Rate Charging: An automatically controlled charging method using either constant current or modified constant potential. Charging starts at a relatively high rate and is automatically reduced to a lower rate when the battery counter-voltage reaches a predetermined value.
U
Useful Acid: The quantity of electrolyte located above the lower edges of the plates that actively participates in the electrochemical reactions occurring during discharge.
V
VRLA: Valve-Regulated Lead-Acid battery. The two main VRLA battery technologies are AGM and Gel.
Vacuum Cell Filler: A filling device used in charging areas that applies vacuum to remove the air displaced by the electrolyte as the cells are filled.
Vent Assembly: A cell-venting unit consisting of a ceramic vent stone and a filling funnel mounted on either a threaded base or a quarter-turn bayonet base.
Vent Baffle: A thin disc located inside a vent cap or plug that redirects electrolyte spray back into the cell.
Vent Plug: The component or group of components used to close the vent and filling opening of a cell cover while leaving a small passage through which gases can escape. Vent plugs are commonly secured by threads, a quarter-turn bayonet mechanism, or a snap-in design.
Vent Well: The opening in the cell cover through which gases are released, electrolyte is added, or the electrolyte level is inspected. The vent plug or vent assembly is installed in this opening.
Volt: The practical unit of electromotive force or potential difference, equal to the potential required to produce a current of one ampere through a resistance of one ohm.
Volt Efficiency: The ratio of the average discharge voltage of a cell or battery to the average voltage applied during the subsequent recharge.
Voltage: The electrical potential difference between the terminals of a cell or battery, or between any two points in an electrical circuit.
Voltage Drop: The difference in electrical potential measured across a resistance or impedance. Its relationship to current is defined by Ohm’s Law.
Voltage Range: The difference between the highest and lowest cell voltages present within a battery or series-connected group of cells while all cells are being charged or discharged.
Voltmeter: Used to measure electrical voltage.
