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Glossary of Battery Definitions

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). V=I/R

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.

Polarization: The voltage drop in a cell during discharge due to the flow of an electrical current. The cell's internal resistance increases with the buildup of a product of oxidation or a reduction of an electrode, preventing further reaction.

Power: Defined by voltage (V) and current (I), P=VI.
Since V=IR, P=I2R and P=V2/R
Power also can be described by energy emitted per unit of time: P=E/t.
Thus E=VIt=qV.

Power density (specific power): Power density is the ratio of the power available from a battery to its volume (watt/liter). Specific power generally refers to the ratio of power to mass (watt/kg). Comparison of power to cell mass is more common.

Primary cells: A cell that is not designed for recharging and is discarded once it has produced all its electrical energy.

Prismatic: Just a word to say that the cells are not cylindrical, as nature intended battery cells to be, but fit nicely into a parallelepiped or any other such flattened shape.

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.

Porous separator: This permeable material or membrane separates the battery's two electrodes and allows current to flow from the positive to the negative electrode.

Positive electrode: This is the conductive part of the battery; electrons flow away from it.

Primary Battery: A battery made up of primary cells. See Primary Cell.

Reserve cell: A cell that may be kept inactive and which is activated by adding an electrolyte or electrode, or melting an electrolyte in a solid state.

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.

Rechargeable battery: This is a battery that can be used repeatedly by adding power to it when the cells are drained. These batteries typically can go through a few hundred charge cycles before they start to lose the ability to hold a charge.

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

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 content.

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 conductor).

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 situations.

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 Secondary Cell.

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.

Secondary cells: A cell capable of repeated use. Its charge may be fully restored by passing an electric current through the cell in the opposite direction to that of discharge, thus reversing the redox reactions.

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 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 not recommended.

Voltage, nominal: Voltage of a fully charged cell when delivering rated current.

Wet Cell: A cell, the electrolyte of which is in liquid form and free to flow and move.

Watt-hour: A watt-hour is a measurement of the amount of energy held in a battery that can power a one-watt device for one hour. Many external batteries have between 100 and 200 watt-hours of energy.

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