Glossary of Terms

MaxAmps Glossary for Batteries, Power Supplies & More

Absorption: Hydrogen retention by the hydrogen-absorbing Misch metal alloys of batteries’ negative electrodes.

Acid Battery: A battery in which acid is used as the electrolyte, e.g., lead-acid battery in which sulfuric acid is the electrolyte.

Active Material: Electrode material which produces electrical energy during discharge from chemical energy stored during charge.

Alkaline Storage Battery: A battery which employs alkaline aqueous solution for its electrolyte. The Nickel-cadmium battery as designed.

Ambient Temperature: The average temperature of the battery's surrounding medium, typically air.

Ampere Hours (Ah): A unit expressing the capacity of a battery or cell. Ampere hours are the product of a battery's or cell's discharge rate and discharge time. It is usually measured in mAh (milli-Amps x hours).

Anode: An electrode where oxidation takes place during electrochemical reaction. Negative electrode is the anode during discharge; positive electrode is the anode during charge.

Assembled Battery: Any battery composed of multiple cells.

Balance Charge: The maximum recommended manufacturer charging rate, when using balance charge mode. Usually listed in A(amps).

Battery (Battery Pack): Two or more electrically connected cells in a series/parallel arrangement, designed to create the desired voltage/capacity. "Battery" is the common term for a single cell.

Brick Configuration: This refers to when the battery pack is assembled in a single stack formation, one cell on top of the other.

Button Cell: A battery cell with overall height less than its diameter. Button cells are manufactured with circular disc electrodes that are separated with a separator sheet.

C: C designates the nominal capacity of the battery. The charge-discharge current is specified in terms of a multiple of C. For example, the 0.1 current for N-1300SC is equal to 1300 X 0.1 = 130mA.

C-Rate: A unit by which charge and discharge times are scaled. The capacity of NiCd batteries is commonly rated at 1C, meaning that a 10000mAh battery would be discharged at 10000mA for one hour.

Cadmium: Chemical symbol: Cd. This metallic element is the chemically-active material of the Nickel-cadmium battery's negative electrode. When the battery is charged, the negative electrode surface consists of cadmium. As the battery discharges, the cadmium progressively changes into cadmium hydroxide (CdOH2).

Cadmium Hydroxide: The active material used at the negative electrode of the Nickel-cadmium cell.

Cadmium Salt: A chemical compound in which the hydrogen atom has been replaced by the cadmium atom: e.g.) 2HNO3 + Cd(OH)2 -> Cd(NO3)2 + 2H2O cadmium nitrate.

Cathode: An electrode where reduction takes place during electrochemical reaction. Positive electrode is the cathode during discharge; negative electrode is the cathode during charge.

Capacity: The maximum amount of electrical current that can be withdrawn from a battery cell under specified conditions. Capacity is the product of discharge rate and discharge time (mAhr = mA x hrs); measured in milli-amp hours (mAh).

Capacity Offset: A correction factor applied to the rating of a battery if discharged under different C-rates from the one rated.

Cell: A cell is the basic electrochemical unit which stores electrical energy or releases stored electrical energy.

Cell-Mismatch: Cells within a battery pack that contain different capacity and voltage levels.

Cell Reversal: The discharging of a cell to a state of reversed polarity.

Change in Temperature: A charge termination based on the difference between ambient temperature and cell temperature.

Change in Temperature/Change in Time (dT/dt): A charge termination based on change in temperature over time. This termination is meant to detect rapid temperature increases created just before a battery or cell reaches its full charge. Normal dT/dt is 1°C/minute.

Charge: The process of replenishing or replacing the electrical charge in a rechargeable cell or battery.

Charge Acceptance: A cell's ability to store energy which can be affected by temperature, charge rate, and state of charge.

Charge Efficiency: The ratio of a cell's output during discharge to its input during charge. Ratio can be expressed in efficiency of capacity, nominal voltage, or power.

Charge Rate: The current applied to a cell to restore its capacity. Charge rate is usually expressed in terms of the cell's C Rate.

Charge Retention: The residual capacity after a period of storage of a fully charged battery.

Charge, State of (SOC): The capacity remaining in a cell or battery.

Chemical Cells: The type of cells which convert energy obtained by chemical reactions into electrical current. Most of the popularly used cells belong to this group.

Constant Voltage Charge: A charge during which the voltage across the battery terminals is maintained at a constant value. This method is not normally used for sealed nickel-cadmium cells or batteries.

Constant Current Charge: A charge during which the current is maintained at a constant value. Sealed nickel-cadmium batteries are normally charged at a constant.

Coulomb: A unit to measure the in-going charge and out-going discharge current of a battery. A coulomb is equal to the electricity transferred by a current of one ampere in one second.

Current-Limiting Chargers: A charger that keeps the charge current constant during the charge process but allows the voltage to fluctuate (typically used on NiCd and NiMH chargers).

Cut-Off Voltage: The specified voltage at which a discharge of a cell or battery is considered finished. (Final voltage)

Cycle: The battery sequence of a discharge followed by a recharge, or a charge followed by a discharge.

Cycle Life: The number of cycles a cell can operate through, under specified conditions, before becoming nonfunctional.

Cycle Use: A method of battery use involving repeated charging and discharging.

Cylindrical Cell: A cell with a circular cross-section and height greater than its diameter. Manufactured by winding electrodes spirally with a separator between them.

Deep Cycling: An application in which the cell or battery is successively and repeatedly charged, then completely and fully discharged.

Deep Discharge: A discharge of at least 80% of the rated capacity of a cell or battery.

Depth of Discharge (DOD): The capacity removed from a battery as compared to its actual capacity. It is expressed in percentage.

Delta V: Detecting the voltage drop which indicates a cell is fully charged. See "negative Delta V (-ΔV)"

Depression: See "memory effect".

Discharge: An operation during which a battery delivers current to an external circuit by the conversion of chemical energy into electrical energy.

Discharge Capacity: The capacity that can be discharged from a battery. The unit as Ah, (ampere-hour).

Discharge Rate: The rate at which electrical current is removed from a cell or battery, usually measured in milli-amperes (mA) or multiples of the C Rate.

Discharge VoltageThe amount of battery voltage available at any given point while the battery is discharging.

Duty Cycle: The operating regime for a battery or cell, including charge and discharge rates, charge termination, depth of discharge, and time in rest mode.

Electrode: The matrices of a battery or cell which provide the sites for the electrochemical process to take place.

Electrolyte: The medium which provides the ion transport mechanism between a battery's or cell's electrodes. Potassium Hydroxide (KOH) is the electrolyte in NiMH batteries, for example.

Electrolyte Retention Capability: The degree to which a separator retains electrolyte.

ETE: This refers to when the battery pack is built in an “end to end” configuration.

End Voltage: The voltage that indicates the end limit of discharge. This voltage is almost equivalent to capacity in practical use.

Endothermic: The heat absorption caused by a chemical reaction.

Energy: The overall amount of power a battery or cell can deliver over time. The product of the battery's or cell's voltage, discharge rate, and discharge time. Usually expressed in milli-Watt hours (mWhr) or mWhr = V x mA x hrs.

Energy Density: A ratio of a battery's or cell's energy to its weight or volume. Also called Power Density. See also "gravimetric energy density" and "volumetric energy density".

Exercise: Commonly understood as one or more discharge cycles to one volt per cell with subsequent recharge. Used to maintain NiCd & NiMH batteries.

Exothermic: The release of heat caused by a chemical reaction.

FAA: The Federal Aviation Administration is an operating mode of the U.S. Department of Transportation.

Fast Charge: The rate of charging a cell or battery to full charge capacity in less than an hour.

Final Voltage: The specified voltage at which a discharge of a battery is considered finished.

First Article Inspection: First article inspection is a requirement for some companies during new product development. It ensures that the manufacturing process is capable of consistently delivering products that meet specifications.

Float Charge: This is similar to trickle charge; compensates for the self-discharge on a SLA battery.

Gas Permeability: The degree of mobility of gas through porous film, fabric or other plate-separating material.

Gas Recombination on Negative Electrode: The method to suppress hydrogen generation by recombining oxygen gas on the negative electrode, and making the negative electrode chemically discharged when oxygen gas is generated at the positive electrode at the end of charging.

Gravimetric Energy Density: The ratio of a battery's or cell's energy to its weight. Also called power density. Usually expressed in Watt-Hours per kilogram (Wh/kg).

High Rate Discharge: Discharging at a comparatively high current rate in comparison with cell capacity.

IATA: The International Air Transport Association represents and serves airlines with advocacy and global standards for safety, security and efficiency.

IEC: The International Electrotechnical Commission, a non-profit, non-governmental international standards organization. Prepares and publishes international standards for all electrical, electronic, and related technologies.

ION: An atom or a group of atoms charged either positively or negatively.

Impedance: This is used in terms of the battery's internal resistance.

Intelligent Battery: A battery with an internal circuit enabling some communication between the battery and user. Some batteries feature a capacity indicator only, others offer an external bus to interface with the equipment the battery powers and the intelligent charger.

Internal Resistance: The opposition or resistance of a battery or cell to an alternating current, usually 1000 Hz. Internal resistance is the ohmic component of a battery's or cell's resistance to the flow of electrical current within the battery or cell.

Internal Pressure: The pressure within a sealed battery or cell caused by oxygen or hydrogen evolution.

Interstitial: A space between closely set things, or between the parts which compose a body. A narrow chink; a crack, crevice, or hole.

IR-DROP: A drop in cell voltage or voltage of inter-cell conductor due to cell internal resistance.

Leakage: The escape of electrolyte to the outer surface of the battery.

Landing Voltage: The recommended voltage for having enough capacity left to safely land the aircraft.

Lithium-ion: An advanced chemistry/technology for primary and secondary batteries. Offers increased performance and energy density over nickel-based batteries. There are several major varieties of lithium-ion battery technology, each of which has unique properties. Lithium-ion allows for very flexible configuration packaging, durable outer casing, and lower cost.

Lithium Iron Phosphate (LiFePO4): The lithium iron phosphate battery or LFP battery is a type of lithium-ion battery using lithium iron phosphate as the cathode material, and a graphitic carbon electrode with a metallic backing as the anode. LFP offers high charge rate capabilities, long cycle life, and safer operation.

Lithium-ion Polymer (LiPo): A lithium-ion polymer battery is a rechargeable battery of lithium-ion technology using a polymer electrolyte instead of a liquid electrolyte. High conductivity semisolid polymers form this electrolyte. LiPo batteries typically offer high-discharge rates but also come in high energy density formats.

Lithium Primary Battery: These have the highest specific energy (energy by weight) and energy density (energy by volume) of all primary battery types. They have open circuit voltages (OCVs) between 2.7 and 3.6V. Their relatively high internal impedance limits them mostly to low drain applications.

Load Current: The discharge current provided by a battery, or drawn by a battery powered device.

Low-Voltage Cutoff: A special sensor which ends discharge at a specified voltage level.

Low-Voltage Disconnect: A voltage-sensing device to automatically disconnect a battery or cell from a load at predetermined voltage. Low-voltage disconnects prevent cell reversal during discharge.

Maintenance Charge (Float Charge): A method for maintaining the charge of a battery or cell by continuously charging it at a rate sufficient to balance its self-discharge.

Manganese Dioxide Lithium: This is generally equivalent to poly batteries and cells in construction, energy density, safety and OCV, though with roughly half the service life. Well-suited to applications with high continuous- or pulse-current requirements due to their lower internal impedance. Available in standard cylindrical and coin styles.

Matching: Grouping individual cells within 2% of capacity to maximize performance and reliability.

Memory: Reversible capacity loss found on NiCd and to a lesser extent on NiMH batteries. The modern definition of memory commonly refers to a change in crystalline formation from the desirable small size to a large size.

Memory Effect (Voltage Depression): The phenomenon in which repeated cycling to less than full discharge results in depression in discharge voltage and loss of capacity of the cell Metal Hydride (MH): negative electrode of a battery or cell. Composed of hydrogen-storing Misch metal alloys.

Migration: The movement of charged ions under the influence of a potential gradient.

Misch Metal (M): A matrix of the negative electrode of a battery or cell. Composed of hydrogen-storing alloys.

Mobility of Ions: The velocity of ions moving in electrolyte between electrodes of opposite polarity.

Negative Delta V (-ΔV): A charge termination based on detecting a decrease in voltage which indicates a cell or battery is charged. It is designed to terminate charge as over-charge starts.

Negative Electrode: An electrode in a battery or cell acting as the anode during discharge. It is composed of hydrogen-storing alloys. Also called the minus electrode.

Nickel Hydroxide: The active material used at the positive electrode of the Nickel-cadmium cell.

Nickel Metal Hydride (NiMH): A battery or cell system comprised of a Nickel (Ni) positive electrode and a metal hydride (MH) electrode.

Nickel Tab: The mechanical connector used to electrically connect cells in a battery pack.

Nominal Capacity: The standard capacity designated by a battery manufacturer to identify a particular cell model.

Nominal Voltage: The average working voltage of a battery or cell which is calculated by multiplying the power (mWh) by the capacity (mAh).

Open Circuit Voltage (OCV): The potential difference between the electrodes of a battery or cell, measured at the terminals in a no-load condition.

Operating Voltage: The voltage between the two terminals of the battery without any load.

Over-Charge: The forcing of current into a battery or cell after all of its active material has been converted into stored energy. AKA, charging beyond full charge.

Over-Discharge: Discharging a battery or cell after all of its stored energy has been released.

Oxygen Recombination: The process in which oxygen generated at the positive electrode of a battery or cell during over-charge reacts with hydrogen at its negative electrode, producing water.

Plastic Bonded Electrodes (PBE): PBE utilizes a manufacturing technique that produces a high-energy density negative electrode that allows higher capacity for a given cell size and a greatly reduced self-discharge.

Parallel: Interconnecting cells, or batteries with like terminals, which are connected to increase the capacity of the resulting battery pack. This resulting battery pack’s capacity is equal to the sum of capacities of the parallel-connected batteries or cells.

Peak/Pulse Discharge: A high-rate discharge, usually of 1 second or less.

Peak Voltage Detection (PVD): An automatic charge termination based on the battery or cell being charged reaching peak voltage. Designed to terminate charge just as over-charge begins.

Permanent Charge: The charging current which can be continuously maintained, regardless of the state of charge of the cell.

Polarity Reversal: Reversing of polarity of the terminals of a cell in a multi-cell battery.

Polarizations: The obstacles to current flow within NiMH cells.

Porosity: The term expressing the porous degree of a sintered plate. The equation for its calculation is: Porosity = (V1/V2) x 100. V1 is the volume of pores and V2 is the total volume of the plate including pores.

Positive Electrode: An electrode of a battery or cell acting as the cathode during discharge. Composed of nickel base (Ni) or nickel hydroxide.

Positive Temperature Coefficient Device (PTC) or Thermostat: A safety device used in battery packs. At a predetermined temperature threshold, internal resistance goes from a low-resistance state to a high-resistance one to provide over-current and over-temperature protection.

Potassium Hydroxide (KOH): An electrolyte providing ion transport mechanism between the electrodes of NiMH cells.

Potential: The energy of an electrical charge which is measured by its power to perform work; electro-motive force. Potential energy per unit charge is voltage.

Potential of Oxygen Evolution: When oxygen gas evolves due to the electrolysis of water in the battery being charged when it reaches a certain potential. This is called the potential of oxygen evolution.

Power: The time rate of energy transfer, measured in Watts (W). Watts equals the product of voltage (V) across a battery or cell and the current (A) through the battery or cell. W = V x A

Primary Battery: A battery or cell that is not rechargeable and that is disposed of once it has delivered all of its electrical energy.

Prismatic Cell: A cell in a slim, rectangular configuration. Manufactured with rectangular electrodes interspaced by separator sheets.

Quantity of Charge: The amount of electric energy supplied to a battery. Its unit is Ah, (ampere-hour.)

Quick Charge: A method of charging a Nickel-cadmium battery for a short time at a high current level.

Rated Capacity: The amount of milli-amperes (mA) a battery or cell can deliver under specified conditions. Rated capacity is measured at C/5 discharge rate to 1 volt @ 25°C after being charged at C/10 for 16 hours.

Recombination: The action by which oxygen gas produced on overcharge is recombined chemically to avoid venting of a sealed cell and loss of water from the electrolyte. See "oxygen recombination"

Recycling: Reclamation of materials without endangering human health and the environment. Nickel-cadmium cells are fully recyclable.

Resealable Safety Vent: A resealable vent built into cylindrical and prismatic cells which prevents the buildup of high internal pressures.

Residual Capacity: The capacity remaining in a battery after field use, prior to charge.

SBS: This refers to when the battery pack is built in a “side by side” configuration.

SLA: SLA stands for sealed led acid. An inexpensive secondary battery using lead.

Sealed Cells: A cell which remains closed and does not release either gas or liquid when operated within the limits of charge and temperature specified by the manufacturer. The cell cannot receive addition to the electrolyte.

Secondary Batteries (Rechargeable): A battery or cell in which passing electrical current through it in the opposite direction of its discharge can reverse the electrochemical process, recharging the battery or cell. Commonly called rechargeable batteries.

Self-Discharge: The loss of energy or capacity in a battery or cell due to internal chemical reactions.

Separator: A separator is ion permeable, electrically nonconductive material which electrically separates the positive and negative electrodes of a battery or cell.

Series: This refers to interconnecting cells, or batteries with like un-terminals that are connected to increase the voltage of the resulting battery pack. This resulting battery pack’s voltage is equal to the sum of voltages of the connected batteries or cells in the series.

Shelf/Storage Life: The duration for which a battery or cell can be stored, under specified conditions, and still retain its performance.

Sintered Electrode: Sintered electrodes were originally developed by Saft, and utilized nickel powder to form a highly porous metal sponge. The pores of this material are impregnated with the active material, yielding high discharge performance and very long life.

Sintered Plaque: A thin nickel-plated grid on which nickel powder has been coated.

Sintered Plate: The plaque on which active materials have been imbedded for charge and discharge reactions.

Slow Charge: Typically an over-night charge lasting about 14 hours at a charge current of 0.1C. The battery does not require instant removal when fully charged.

Soft Cell: A cell whose voltage rises above its defined boundaries during charging. This voltage rise may be caused by high cell impedance as a result of prolonged battery storage, very cold battery temperature, or lack of electrolyte.

Stand-by Use: The use of cells or batteries in which they are constantly charged so as to be always ready for use.

Standard Charge: The maximum recommended manufacturer charging rate, without balancing. Usually listed in A(amps).

State of Charge (SOC): The ratio of electricity, usually expressed as a percentage of available capacity, remaining in a battery or cell on discharge compared to its rated capacity.

Sulfation: The growth of lead sulfate crystals in SLA batteries which inhibits current flow. Sulfation is caused by storage at low state of charge.

Sulfur Dioxide Lithium: Sulfur Dioxide Lithium is used almost exclusively in military/aerospace applications. These cells have somewhat lower energy density than manganese dioxide lithium or poly lithium cells. Service life and energy density are generally less than half that of thionyl chloride lithium cells. It requires emergency vent structures for safety reasons.

Tab: The mechanical lug used to connect cells together to form a battery or to connect it to equipment.

Temperature Cut-Off (TCO): TCO is the secondary charge termination at a specified temperature; used in timed, rapid, and fast charge systems.

Thermal Fuse: A one-time, non-resettable fuse used to protect against over-current Thermal runaway.

Thermal Runaway: A critical condition arising during short-circuit or constant voltage charging in which the current and the temperature of the battery produce a cumulative mutually-reinforcing effect which further increases them and can lead to the destruction of the battery.

Thermostat: A circuit protection device used to prevent over-current and over-temperature. A thermostat will go from a low-resistance state to an open circuit at a predetermined temperature.

Thermistor: A temperature sensing device, used to measure the temperature of a battery pack or cell. A thermistor is typically a Negative Temperature Coefficient (NTC) device which exhibits a predictable and precise decrease in resistance with an increase in temperature.

Three Phase Zone: The area where 3 phases (gas, liquid, and solid) contact with each other. Reactions of substances composing these 3 phases takes place easily.

Time Charge: A charging method, terminated after a predetermined amount of time, designed to charge a battery or cell within 6 to 16 hours.

Top-Off Charge: A charge step designed to fully charge a battery or cell when a rapid or fast charge termination that does not reach 100% SOC is used.

Transport: The movement of ions within a cell. Cations carry net-positive charges; anions carry net-negative charges.

Trickle Charge: see "maintenance charge".

Voltage Cutoff: An electronics board which disconnects the load from a battery pack.

Voltage Limit: A voltage value a battery is not permitted to rise above on charge and/or fall below on discharge.

Voltage-Limiting Charger: A charger that limits the maximum voltage to a battery but allows the current to drop while maintaining the voltage limit. A voltage limiting charge normally also includes current limiting. (Typically used on SLA and Li-ion chargers).

Volumetric Energy Density: The ratio of a cell's energy to its total volume. Usually expressed in Watt-hours per liter (Wh/l). Also called "power density".

Watt Hours (Wh): The amount of electric energy that can be withdrawn from a battery or cell under specified conditions. This energy is measured in milli-Watt-hours (mWh) which is the product of the discharge voltage, discharge rate, and discharge time.