- A rechargeable battery or cell (see also
Ampere or Amp - An Ampere or an Amp is a unit of
measurement for an electrical current. One amp is the amount of
current produced by an electromotive force of one volt acting
through the resistance of one ohm. Named for the French
physicist Andre Marie Ampere. The abbreviation for Amp is A but
its mathematical symbol is "I". Small currents are measured in
milli-Amps or thousandths of an Amp.
Amp Hour or Ampere-Hour - A unit of measurement of a
battery's electrical storage capacity. Current multiplied by
time in hours equals ampere-hours. One amp hour is equal to a
current of one ampere flowing for one hour. Also, 1 amp hour is
equal to 1,000 mAh
Ampere-Hour Capacity - The number of ampere-hours
which can be delivered by a battery on a single discharge.
Anode - During discharge, the negative electrode of the cell
is the anode. During charge, that reverses and the positive
electrode of the cell is the anode. The anode gives up electrons
to the load circuit and dissolves into the electrolyte.
Aqueous Batteries - Batteries with water-based
electrolytes. The electrolyte may not appear to be liquid since
it can be absorbed by the battery’s separator.
Actual Capacity or Available Capacity - The total
battery capacity, usually expressed in ampere-hours or
milliampere-hours, available to perform work. The actual
capacity of a particular battery is determined by a number of
factors, including the cut-off voltage, discharge rate,
temperature, method of charge and the age and life history of
Battery - An electrochemical device used to store
energy. The term is usually applied to a group of two or more
electric cells connected together electrically. In common usage,
the term “battery” is also applied to a single cell, such as a
Battery Capacity - The electric output of a cell or
battery on a service test delivered before the cell reaches a
specified final electrical condition and may be expressed in
ampere-hours, watt- hours, or similar units. The capacity in
watt-hours is equal to the capacity in ampere-hours multiplied
by the battery voltage.
Battery Charger - A device capable of supplying
electrical energy to a battery.
Battery-Charge Rate - The current expressed in amperes
(A) or milli amps (mA) at which a battery is charged.
Cutoff Voltage, final - The prescribed lower-limit
voltage at which battery discharge is considered complete. The
cutoff or final voltage is usually chosen so that the maximum
useful capacity of the battery is realized. The cutoff voltage
varies with the type of battery and the kind of service in which
the battery is used. When testing the capacity of a NiMH or NiCD
battery a cutoff voltage of 1.0 V is normally used. 0.9V is
normally used as the cutoff voltage of an alkaline cell. A
device that is designed with too high a cutoff voltage may stop
operating while the battery still has significant capacity
C - Used to signify a charge or discharge rate equal
to the capacity of a battery divided by 1 hour. Thus C for a
1600 mAh battery would be 1.6 A, C/5 for the same battery would
be 320 mA and C/10 would be 160 mA. Because C is dependent on
the capacity of a battery the C rate for batteries of different
capacities must also be different.
Capacity - The capacity of a battery is a measure of
the amount of energy that it can deliver in a single discharge.
Battery capacity is normally listed as amp-hours (or milli
amp-hours) or as watt-hours.
Cathode - Is an electrode that, in effect, oxidizes
the anode or absorbs the electrons. During discharge, the
positive electrode of a voltaic cell is the cathode. When
charging, that reverses and the negative electrode of the cell
is the cathode.
Cell - An electrochemical device, composed of positive
and negative plates and electrolyte, which is capable of storing
electrical energy. It is the basic “building block” of a
Charge - The conversion of electric energy, provided
in the form of a current, into chemical energy within the cell
Charge Rate - The amount of current applied to battery
during the charging process. This rate is commonly expressed as
a fraction of the capacity of the battery. For example, the C/2
Charging - The process of supplying electrical energy
for conversion to stored chemical energy.
Constant-Current Charge - A charging process in which
the current applied to the battery is maintained at a constant
Constant-Voltage Charge - A charging process in which
the voltage applied to a battery is held at a constant value.
Cycle - One sequence of charge and discharge.
Deep Cycle - A cycle in which the discharge is
continued until the battery reaches it’s cut-off voltage,
usually 80% of discharge.
Shallow Cycling - Charge and discharge cycles which do
not allow the battery to approach it’s cutoff voltage. Shallow
cycling of NiCd cells lead to “memory effect”. Shallow cycling
is not detrimental to NiMH cells and it is the most beneficial
for lead acid batteries.
Cycle Life - For rechargeable batteries, the total
number of charge/discharge cycles the cell can sustain before
it’s capacity is significantly reduced. End of life is usually
considered to be reached when the cell or battery delivers only
80% of rated ampere- hour capacity. NiMH batteries typically
have a cycle life of 500 cycles, NiCd batteries can have a cycle
life of over 1,000 cycles. The cycle of a battery is greatly
influenced by the type depth of the cycle (deep or shallow) and
the method of recharging. Improper charge cycle cutoff can
greatly reduce the cycle life of a battery.
Direct Current (DC) - The type of electrical current
that a battery can supply. One terminal is always positive and
another is always negative.
Discharge - The conversion of the chemical energy of
the battery into electric energy.
Depth of Discharge - The amount of energy that has
been removed from a battery (or battery pack). Usually expressed
as a percentage of the total capacity of the battery. For
example, 50% depth of discharge means that half of the energy in
the battery has been used. 80% DOD means that eighty percent of
the energy has been discharged, so the battery now holds only
20% of its full charge.
Discharge, deep - Withdrawal of all electrical energy
to the end-point voltage before the cell or battery is
Discharge, high-rate - Withdrawal of large currents
for short intervals of time, usually at a rate that would
completely discharge a cell or battery in less than one hour.
Discharge, low-rate - Withdrawal of small currents for
long periods of time, usually longer than one hour.
Drain - Withdrawal of current from a cell.
Dry Cell - A primary cell in which the
electrolyte is absorbed in a porous medium, or is otherwise
restrained from flowing. Common practice limits the term “dry
cell” to the Leclanch‚ cell, which is the common commercial
Electrochemical Couple - The system of active
materials within a cell that provides electrical energy storage
through an electrochemical reaction.
Electrode - An electrical conductor through which an
electric current enters or leaves a conducting medium, whether
it be an electrolytic solution, solid, molten mass, gas, or
vacuum. For electrolytic solutions, many solids, and molten
masses, an electrode is an electrical conductor at the surface
of which a change occurs from conduction by electrons to
conduction by ions. For gases and vacuum, the electrodes merely
serve to conduct electricity to and from the medium.
Electrolyte - A chemical compound which, when fused or
dissolved in certain solvents, usually water, will conduct an
electric current. All electrolytes in the fused state or in
solution give rise to ions which conduct the electric current.
Electropositivity - The degree to which an element in
a galvanic cell will function as the positive element of the
cell. An element with a large electropositivity will oxidize
faster than an element with a smaller electropositivity.
End-of-Discharge Voltage - The voltage of the battery
at termination of a discharge.
Energy - Output Capability - expressed as capacity
times voltage, or watt-hours.
Energy Density - Ratio of cell energy to weight or
volume (watt-hours per pound, or watt-hours per cubic inch).
Final Voltage (see Cutoff voltage)
Float Charging - Method of recharging in which a
secondary cell is continuously connected to a constant-voltage
supply that maintains the cell in fully charged condition.
Typically applied to lead acid batteries.
Galvanic Cell - A combination of electrodes, separated
by electrolyte, that is capable of producing electrical energy
by electrochemical action.
Gassing - The evolution of gas from one or both of the
electrodes in a cell. Gassing commonly results from
self-discharge or from the electrolysis of water in the
electrolyte during charging.
Internal Resistance - The resistance to the flow of an
electric current within the cell or battery.
Memory Effect - A phenomenon in which a cell, operated
in successive cycles to less than full, depth of discharge,
temporarily loses the remainder of its capacity at normal
voltage levels (usually applies only to Ni-Cd cells). Note,
memory effect can be induced in NiCd cells even if the level of
discharge is not the same during each cycle. Memory effect is
Negative Terminal - The terminal of a battery from
which electrons flow in the external circuit when the cell
discharges. See Positive Terminal.
Nonaqueous Batteries - Cells that do not contain
water, such as those with molten salts or organic electrolytes.
Ohm’s Law - The formula that describes the amount of
current flowing through a circuit. Ohm's Law - In a given
electrical circuit, the amount of current in amperes (I) is
equal to the pressure in volts (V) divided by the resistance, in
ohms (R). Ohm's law can be shown by three different formulas:
To find Current I = V/R
To find Voltage V = I x R
To find Resistance R = V/I
Open Circuit - Condition of a battery which is neither
on charge nor on discharge (i.e., disconnected from a circuit).
Open-Circuit Voltage - The difference in potential
between the terminals of a cell when the circuit is open (i.e.,
a no-load condition).
Oxidation - A chemical reaction that results in the
release of electrons by an electrode’s active material.
Parallel Connection - The arrangement of cells in a
battery made by connecting all positive terminals together and
all negative terminals together. The voltage of the group
remains the same as the voltage of the individual cell. The
capacity is increased in proportion to the number of cells.
Polarity - Refers to the charges residing at the
terminals of a battery.
Positive Terminal - The terminal of a battery toward
which electrons flow through the external circuit when the cell
discharges. See Negative Terminal.
Primary Battery - A battery made up of primary cells.
See Primary Cell.
Primary Cell - A cell designed to produce electric
current through an electrochemical reaction that is not
efficiently reversible. The cell, when discharged, cannot be
efficiently recharged by an electric current. Alakline, lithium,
and zinc air are common types of primary cells.
Rated Capacity - The number of ampere-hours a cell can
deliver under specific conditions (rate of discharge, end
voltage, temperature); usually the manufacturer’s rating.
Rechargeable - Capable of being recharged; refers to
secondary cells or batteries.
Recombination - State in which the gases normally
formed within the battery cell during its operation, are
recombined to form water.
Reduction - A chemical process that results in the
acceptance of electrons by an electrode’s active material.
Seal - The structural part of a galvanic cell that
restricts the escape of solvent or electrolyte from the cell and
limits the ingress of air into the cell (the air may dry out the
electrolyte or interfere with the chemical reactions).
Secondary Battery - A battery made up of secondary
cells. See Storage Battery; Storage Cell.
Self Discharge - Discharge that takes place while the
battery is in an open-circuit condition.
Separator - The permeable membrane that allows the
passage of ions, but prevents electrical contact between the
anode and the cathode.
Series Connection - The arrangement of cells in a
battery configured by connecting the positive terminal of each
successive cell to the negative terminal of the next adjacent
cell so that their voltages are cumulative. See Parallel
Shelf Life - For a dry cell, the period of time
(measured from date of manufacture), at a storage temperature of
21 degrees C (69 degrees F), after which the cell retains a
specified percentage (usually 90%) of its original energy
Short-Ciruit - A condition that occurs when a short
electrical path is unintentionally created. Batteries can supply
hundreds of amps if short-circuited, potentially melting the
terminals and creating sparks.
Short-Circuit Current - That current delivered when a
cell is short-circuited (i.e., the positive and negative
terminals are directly connected with a low-resistance
Starting-Lighting-Ignition (SLI) Battery - A battery
designed to start internal combustion engines and to power the
electrical systems in automobiles when the engine is not
running. SLI batteries can be used in emergency lighting
Stationary Battery - A secondary battery designed for
use in a fixed location.
Storage Battery - An assembly of identical cells in
which the electrochemical action is reversible so that the
battery may be recharged by passing a current through the cells
in the opposite direction to that of discharge. While many
non-storage batteries have a reversible process, only those that
are economically rechargeable are classified as storage
batteries. Synonym: Accumulator; Secondary Battery. See
Storage Cell - An electrolytic cell for the generation
of electric energy in which the cell after being discharged may
be restored to a charged condition by an electric current
flowing in a direction opposite the flow of current when the
cell discharges. Synonym: Secondary Cell. See Storage Battery.
Taper Charge - A charge regime delivering moderately
high-rate charging current when the battery is at a low state of
charge and tapering the current to lower rates as the battery
becomes more fully charged.
Terminals - The parts of a battery to which the
external electric circuit is connected.
Thermal Runaway - A condition whereby a cell on charge
or discharge will destroy itself through internal heat
generation caused by high overcharge or high rate of discharge
or other abusive conditions.
Trickle Charging - A method of recharging in which a
secondary cell is either continuously or intermittently
connected to a constant-current supply that maintains the cell
in fully charged condition.
Vent - A normally sealed mechanism that allows for the
controlled escape of gases from within a cell.
Volt - The unit of measurement of electromotive force,
or difference of potential, which will cause a current of one
ampere to flow through a resistance of one ohm. Named for
Italian physicist Alessandro Volta (1745-1827).
Voltage, cutoff - Voltage at the end of useful
discharge. (See Voltage, end-point.)
Voltage, end-point - Cell voltage below which the
connected equipment will not operate or below which operation is
Voltage, nominal - Voltage of a fully charged cell
when delivering rated current.
Watt - A measurement of total power. It is amperes
multiplied by volts. 120 volt @ 1 amp = 12 volts @ 10 amps.
Wet Cell - A cell, the electrolyte of which is in
liquid form and free to flow and move.