The electrode from which electrons flow when the battery is discharging into an
external circuit. Reactants are electrochemically oxidized at the negative electrode. In the lead-acid
cell, the negative electrode contains spongy lead and lead sulfate (PbSO4) as the active materials.
In the nickel-cadmium cell, the negative electrode contains cadmium and cadmium hydroxide
(Cd(OH)2) as the active materials.
The characteristic operating voltage of a cell or battery. The nominal voltage is 2.0 V
for lead-acid cells and 1.2 V for nickel-cadmium cells. These voltage levels represent the approxi-
mate cell voltage during discharge at the C-rate under room-temperature conditions. The actual
discharge voltage depends on the state-of-charge, state-of-health, discharge time, rate, and tem-
The electrode to which electrons flow when the battery is discharging into an external
circuit. Reactants are electrochemically reduced at the positive electrode. In the lead-acid cell, the
positive electrode contains lead dioxide (PbO2) and lead sulfate (PbSO4) as the active materials.
In the nickel-cadmium cell, the positive electrode contains nickel oxyhydroxide (NiOOH) and
nickel hydroxide (Ni(OH)2) as the active materials.
An electrically insulating material that is used to prevent metallic contact between the positive
and negative plates in a cell, but permits the flow of ions between the plates. In flooded cells, the
separator includes a gas barrier to prevent gas diffusion and recombination of oxygen. In sealed
cells, the separator is intended to allow gas diffusion to promote high recombination efficiency.
The available capacity of a battery divided by the capacity available when fully charged,
normally expressed on a percentage basis. Sometimes referred to as “true state-of-charge.’’
The available capacity of a fully charged battery divided by the rated capacity of the
battery, normally expressed on a percentage basis. Sometimes referred to as “apparent state-of-
charge.” Can also be used in a more qualitative sense to indicate the general condition of the battery.
The quantity of stored electrical energy, measured in ampere-hours, that the
battery can deliver from its completely charged state to its discharged state. The dischargeable capacity
depends on the rate at which the battery is discharged; at higher discharge rates the available
capacity is reduced.
The discharge rate, in amperes, at which a battery can deliver 1 h of capacity to a fixed voltage
endpoint (typically 18 or 20 V for a 24-V battery). Fractions or multiples of the C-rate also are
used. C/2 refers to the rate at which a battery will discharge its capacity in 2 h; 2C is twice the C-
rate or that rate at which the battery will discharge its capacity in 0.5 h. This rating system helps
to compare the performance of different sizes of cells.
The numerical value of the current, in amperes, that a fully charged lead-acid battery can deliver
at 18°C (0°F) for 30 s to a voltage of 1.2 V per cell (i.e., 14.4 V for a 24-V battery). In some cases,
60 s is used instead of 30 s. CCA stands for cold cranking amperes.
An ionically conductive, liquid medium that allows ions to flow between the positive and
negative plates of a cell. In lead-acid cells, the electrolyte is a mixture of sulfuric acid (H2SO4) and
deionized water. In nickel-cadmium cells, the electrolyte is a mixture of potassium hydroxide
(KOH) dissolved in deionized water.
The numerical value of the current, in amperes, delivered after 15 s during a constant voltage
discharge of 0.6 V per cell (i.e., at 12 V for a 24-V battery). The Imp rating normally is based on
a battery temperature of 23°C (75°F), but manufacturers generally can supply Imp data at lower
temperatures as well.
A group of two or more cells connected in series and housed in a one-piece enclosure with
suitable dividing walls between cell compartments. Typical monoblocs come in 6-V, 12-V, or 24-v
configurations. Monoblocs are commonly used in lead-acid batteries, but rarely used in nickel-
cadmium aircraft batteries.
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