Glossary
Active material - The material which reacts chemically to produce electric energy when the cell disharges, and which is restored to its original state during the charge.
Alkaline storage battery - A batery 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 measure of energy that is provided to, or drawn from a battery (a curent of one ampere for one hour equals 1 Ah).
Assembled battery - Any battery composed of multiple cells.
Battery - Two or more cels connected together and used as a source of electric energy.
Button cell - A cell of circular cross-section in which the overall height is less than the diameter. A sealed nickel-cadmium button cell is comprised of positive and negative electrodes, a separator, alkaline electrolyte and metal case.
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 - 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 synbol: 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 disharges, the cadmium progressively changes into cadmium hydroxide (CdOH2).
Cadmium hydroxide - Active material used at the negative electrode of the Nickel-cadmium cell.
Cadmium salt - A chemical compound in which the hydrogen atom as been replaced by the cadmium atom:
(e.g.) 2HNO3 + Cd(OH)2 -> Cd(NO3)2 + 2H2O cadmium nitrate.
Capacity - The electric energy content of a battery expressed in ampere hours. The energy is referenced to the discharge at a constant current for a measured period of time unitl a specified cut-off voltage is reached.
Capacity offset - A correction factor applied to the rating of a battery if discharged under different C-rates from the one rated.
Cell - The basic unit of a battery . It is an electrochemical device capable of storing electric energy.
Cell-mismatch - Cells within a battery pack that contain different capacity and voltage levels.
Cell reversal - A condition in which the overdischarge of a battery causes one or more cels to cjange the normal polarity. Normally, at least three cells are required in series for the condition to exist.
Charge - The process of replenishing or replacing the electrical charge in a rechargeable cell or battery.
Charge efficiency - The value which can be obtained when the dishargeable capacity of the battery is divided by the charged capacity. It indicates the degree of ease with which the battery can be charged.
Charge rate - The current at which a cell or battery is charged. Generally expressed as a function of rated capacity. For instance, a charge rate of (0.4A for a 4Ah cell or battery is equal to C/10 or 0.1C5A).
Charge retention - Residual capacity after a period of storage of a fully charged battery.
Charge, state of - 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 popualrly 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. (The maximu energy a molecular weight of a chemical system can deliver is one Faraday of energy or 96,500 coulombs which is the equivelent of 26.8Ah of capacity.
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 disharge of a cell or battery is considered finished. (Final voltage)
Cycle - A process consisting of a single charge and discharge of a rechargeable battery.
Cycle life - The number of cycles a battery can provide before it is no longer usable (a battery is considered non-usable if its nominal capacity falls below 60-80%).
Cycle use - A method of battery use involving repeated charging and discharging.
Cylindrical cell - The positive and negative plates are rolled up and placed into a cylindrical container (as opposed to stacking the plates in a prismatic cell design).
Deep cycling - Application in which the cell or battery is successively and repeatedly charged, then completely and fully discharged.
Deep disharge - Disharge of at least 80% of the rated capacity of a cell or battery.
Depth of discharge - 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.
Disharge - An operation during which a battery delivers current to an external circuit by the conversion of chemical energy into electrical energy.
Disharge capacity - Capacity that can be discharged from a battery. The unit as Ah, (ampere-hour).
Disharge rate - The discharge rate is the rate at which current is removed from a battery. When a battery is discharged at a current level "i", for a period until the end discharge voltage is reached "h", the discharge is referred to as the h-hour rate discharge, while "i" is know as the h-hour rate discharge current. For practical use, nominal capacity is used as the standard.
Discharge voltage - The voltage between the terminals of a cell or battery under load, during disharge.
Duty cycle - The normal use of a cell or battery in its application, including charge, disharge, rest and overcharge.
Electrode - Conducting element within a cell in which an electrochemical reaction occurs. Normally includes active materials plus conductive and supportive elements. The positive or negative plate holding active materials.
Electrolyte - The chemical compound or solution that allows ions (electrically-charged particles) to be conducted between the electrodes of a battery. In the Nickel-cadmium battery, a solution of potassium hydroxide (KOH) or sodium hydroxide (NaOH) is utilized.
Electrolyte retention capability - The degree to which a separator retains electrolyte.
End voltage - The voltage that indicates the end limit of discharge. This voltage is almost equivelent to capacity in practical use.
Energy - Watts (voltage x current) multiplied by time.
Energy density - The amount of energy a cell can contain. Gravimetric energy is the Watt-hours a battery is capable of providing per given weight (pound or Kg); and volumetric energy is the Watt-hours per given size (cubic inch or cubic centimeter). The energy is defined as nominal battery voltage multiplied by rated capacity.
Exercise - Commonly understood as one or more discharge cycles to one volt per cell with subsequent recharge. Used to maintain NiCd & NiMH batteries.
Fast charge - Typical fast charge time for a NiCd is 1 to 3 hours. The fast-charger detects the state of charge and switches to trickle charge when full-charge is reached.
Final voltage - The specified voltage at which a disharge of a battery is considered finished.
Float charge - Similar to trickle charge. Compensates for the self-discharge on a SLA battery.
Foam - Positive electrode made with a porous nickel metal instead of a nickel sintered strip. Thicker and porous, it holds more active material greatly increasing it's capacity.
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.
High rate discharge - Discharge at a comparatively high current rate in comparison with cell capacity.
Hour rate - The hour rate is associated with both discharging and charging the battery, and is expressed in terms of discharge timeat its nominal capacity rating. "H-hou" represents the length of time it takes to discharge a battery, and "i" represents the rate of discharge.
IEC - International Electrotechnical Commission. Sets worldwide standards for the electrotechnical industry. The main IEC standards applicable to sealed nickel-cadmium cells and batteries are:
ION - An atom or a group of atoms charged either positively or negatively.
Impedance - Used in terms of the battery's internal resistance.
Intelligent battery - Battery withinternal 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 quotient of the change of voltage of a cell or battery to the corresponding change of currentunder specified conditions. Alternating current(AC) and direct current(DC) measurment methods lead to very different values. The AC internal resistance is usually measured at 1000 Hz.
Internal pressure - The pressure which exists within a sealed cell.
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.
Load current - The discharge current provided by a battery, or drawn by a battery powered device.
Low-voltage cutoff - A special sensor which ends disharge at a specified voltage level.
Matched cells - Cells carefully selected by the factory to display within 5% of the same capacity at the time of manufacturer.
Memory - Reversible capacity loss found on NiCd and to a lesser extend 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.
Mobility of ions - Velocity of ions moving in electrolyte bewteen electrodes of oposite polarity.
Negative Delta V (NDV) - The NDV is a drop in the battery voltage which occurs when a sealed NiCd and NiMH battery reaches the full charge state. The NDV of a NiMH is smaller than that of the NiCd and by itself is not reliable in terminating the fast charge of a NiMH battery.
Negative electrode - The plate which has an electrical potential lower than that of the other plate during normal cell operation. Electric current from the external circuit flows into the cell at the electrode during discharge. Also called the minus electrode.
Nickel hydroxide - Active material used at the positive electrode of the Nickel-cadmium cell.
Nickel Metal Hydride (Ni-MH) - New battery technology providing increased volumetric . An original system comprising a nickel positive electrode and metal hydride (HM) negative electrode.
Nominal capacity - The standard capacity designated by a battery manufacturer to indentify a particular cell model.
Nominal voltage - A given voltage of a cell that is accepted as an industrial standard. (Cell voltages of 1.20 and 1.25 volts are used for NiCd and NiMH batteries.
Open-circuit voltage - The no-load voltage of a cell or battery measured with a high-impedance voltmeter at a temperature of 20° C.
Operating voltage - Voltage between the two terminals of the battery without any load.
Overcharge - Continuous charging of a battery after it reaches full charge. The battery can no longer absorb any further charge and the charge current turns into heat, causing damage to the battery.
Over discharge - To discharge a battery to a level below the predetermined end voltage.
Overvoltage - The difference between the actual potential of electro-chemical reaction and the theoretical value at which the reaction becomes balanced.
PBE - Plastic Bonded Electrodes. 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 disharge.
Parallel - Connection of the cell terminals of the same polarity together to form a battery of higher capacity. Parallel connection is not recommended for sealed nickel-cadmium cells or batteries except under special controlled conditions.
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 small-capacity cell in a multi-cell battery due to overdischarge.
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 - The electrode which has a positive potential. Electric current from this electrode flows in the external circuit during discharge.
Potassium hydroxide - The electrolytr normally used in nickel-cadmium cells and batteries. Referred to as KOH.
Potential of oxygen evolution - 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.
Primary battery - A battery that is non-rechargeable. The active materials on a primary battery are irreversibly converted during the chemical reaction which produces energy.
Prismatic cell - A slim, rectangular sealed cell in a metal case with lasser-welded cover with a resealable safety vent. The positive and negative plates are stacked rather than rolled as done in a cyclindrical cell.
Pulse disharge - A high-rate disharge, usually of 1 second or less.
Quantity of charge - The amount of electric energy supplied to a battery. Its unit is Ah, (ampere-hour.)
Quick charge - A method of charge an Nickel-cadmium battery for a short time at a high current level.
Rapid charge - A charge time that is bewteen slow charge and fast charge (typically 3 to 6 hours for a NiCd). Rated capacity - The quantity of electricity, declared by the manufacturer which a cell or battery can deliver under specified conditions after a full charge.
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.
Recondition - One or more deep discharge cycles below 1.0 volt/cell ata very low, controlled current. Recondition helps to revert large crystals to small desirable sizes, often restoring the battery to its full capacity.
Recycling - Reclamation of materials without endangering human health and the environment. Nickel-cadmium cells are fully recyclable.
Resealable safety vent - The resealable safety device built into a cell to prevent dangerously high internal pressure.
Residual capacity - The capacity remaining in a battery after field use, prior to charge.
Reversal charge - The Nickel-cadmium cell is reverse-charged when connected to a charger in the wrong way, and current is forced to flow from the negative to positive electrodes, contrary to the direction of flow during normal charge. Here polarity is reversed, but all electric energy is consumed to generate gas.
Reverse load charge - Charge method that intersperses discharge pulses between charge pulses to promote the recombination of gases generated during fast charge. Reverse Load charge also helps to reduce memory.
Safety vent - A safety mechanism that is activated when the internal gas pressure rises above a normal level. There are two types: Automatically resealable, and unresealable.
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 battery - A battery which can be recharged and used repeatedly.
Self-discharge - Capacity loss during storage due to the internal leakage between the positive and negative cell plates.
Separator - A film to separate 2 electrodes to prevent short-circuiting and retain electrolyte.
Series - The connection of positive to negative of two or more cells to form a battery. The usual installation arrangement of sealed nickel-cadmium cells.
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 disharge 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. 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 normal C/10 charge used to recharge a cell or battery in 16 hours. Sometimes called an overnight charge.
State of charge - The available capacity of a cell or battery at any given time. Expressed as a percentage of C or its rated capacity.
Step charge method - One of the charging methods where the charge current is varied stepwise during charge.
Storage life - The length of time a cell or battery can be stored on open circuit without permanent deterioration of its performance. Nickel-cadmium cells or batteries can be stored at any state of charge including a fully disharged state.
Sulfation - Growth of lead sulfate crystals in SLA batteries which inhibits current flow. Sulfation is caused by storage at low state of charge.
Tab - The mechanical lug used to connect cells together to form a battery or to connect it to equipment.
Temerature cutoff - A temperature sensing method which detects heat rise in a cell at overcharge and switches the charger off or to a lower rate of charge.
Thermal runaway - A critical condition arising during 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.
Three phase zone - The area where 3 phases, gas kiquid, and solid, contact with each other, Reactions of substances composing these 3 phases take place easily.
Trickle charge - A continuous charge at low rate which compensates for self-disharge and thus maintains the battery in an approximately fully charged state, normally at a C/20 to C/30 rate.
Voltage cutoff - A voltage sensing device which will end a charge or disharge at a preset voltage value.
Voltage delay - During open circuit storage, some battery ssytems develop a passivation film on the surface of the active material. On the initial discharge, these batteries may momentarily demonstrate a lower than normal voltage until this film is removed by the discharge.
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).
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