Battery Terminology

Battery Terminology

ABS Resin

A plastic material largely used for the case and cover of batteries.

Active Material

The substance which electrochemically reacts in the electrode of batteries.
Lead-acid batteries adopt lead dioxide for the positive electrode and spongy lead for the negative electrode.

Ambient Temperature

Average temperature in the vicinity of the battery.

Available Capacity

The capacity actually available from a cell/battery. The available capacity is the capacity of a battery when it discharges at a specified hour rate, and expressed in hour rate and Ah.

Bolt Fastening Terminal

A type of battery terminals, to which lead wires are connected with bolts.

Built-In Thermostat

The built-in thermostat is a resettable switch built in a battery for temporarily cut off the battery circuit when the temperature of the battery exceeds a preset value or when the battery charges/discharges at a higher rate than predetermined.


Capacity represents the specific energy in ampere-hours (Ah). Manufacturers often overrate a battery by giving a higher Ah rating than it can provide. You can use a battery with different Ah (but correct voltage), provided the rating is high enough. Chargers have some tolerance to batteries with different Ah ratings. A larger battery will take longer to charge than a small one.


The minimum battery unit which composes a storage battery. Nominal voltage of the cell of the lead-acid battery is 2V.


The operation of supplying a battery with a DC current from an external power source to have the electrode active materials conduct chemical reactions then to store electric energy as chemical energy in the battery.

Charge Acceptance Test

Test of batteries to check whether or not they are adequately recharged after discharge.

Charging Efficiency

General term for ampere-hour efficiency and watthour efficiency. In many cases, however, it means the ampere-hour efficiency.


The most common chemistries are lead, nickel and lithium. Each system requires its own charging algorithm. Unless provisions are made to change the charge setting, different battery chemistries cannot be interchanged in the same charger. Also observe the chemistry when shipping and disposing of batteries; each type has a different regulatory requirement.

Cold Cranking Amps(CCA)

CCA specifies the ability to draw high load current at –18°C (0°F) on starter batteries. Different norms specify dissimilar load durations and end voltages.

Constant Current Charge

A method of charging: to charge a battery with a constant current.

Constant Voltage Charge

A method of charging: to charge a battery by applying a constant voltage to the terminals.


A charge or discharge current rate expressed inA or mA. It is numerically the same as the hour rate capacity of a battery expressed inAh of the rated capacity. C-rates specify charge and discharge currents. At 1C, the battery charges and discharges at a current that is par with the marked Ah rating; at 0.5C the current is half, and at 0.1C it is one tenth. On charge, 1C charges a good battery in about one hour; 0.5C takes 2 hours and 0.1C 10 to 14 hours.

Cut-Off Voltage of Discharge

The terminal voltage of a battery at which discharging should be discontinued. This voltage depends on discharge current, type of electrodes and construction of battery.

Cycle Life

The number of charge/discharge/rest cycles a cell/battery can provide. Cycle life is usually expressed by the number of cycles available before duration of discharge decreases to a half of the initial value.

Depth of Discharge

A value to express the state of discharge of a battery. The depth of discharge is generally expressed by the ratio of discharge amount to rated capacity of the battery.


To draw off the electric energy stored in a cell/battery.

Discharge Rate

The term to express the magnitude of discharge current. When assuming discharge current and time to discharge cut-off voltage t hours, this discharge is called t hour rate (tHR) discharge, and the current is called t-hour rate discharge current. When time t is minutes instead of hours, tMR is used.

Duty Cycle Test

Test of batteries in ordinary use including charge, discharge and rest.


The medium which serves to conduct ions in the electrochemical reactions in batteries. The leadacid battery adopts diluted sulfuric acid as the electrolyte.

Energy Density

Energy available per unitApprox. mass or unit volume of a cell/ battery. Energy density is expressed in Wh/kg or Wh/l.

Float Charge

The system in which a constant voltage is continuously applied to a battery connected to a rectifier in parallel with a load to maintain the battery in charged state: on occurrence of power failure or load variation, the battery supplies power to the load without any short break.

Gas Recombinationability

Capability of a battery to recombine (or absorb) internally generated oxygen gas at the negative plate. The greater this capability is, the larger the available charge current.

High Rate Discharge

A very rapid discharge of a battery. (In many cases it means discharging at approx. 1 CA or higher rate.)

Internal Pressure

The pressure within a sealed battery. Internal pressure of a battery is increased by oxygen gas which is generated from the positive plate at the end of charging.

Internal Resistance

The resistance within a battery: it is the total of individual resistances of the electrolyte and the positive and negative plates. Internal resistance is simply measured with the current four-terminal method (1,000 Hz) and expressed in the composite value of resistance component and capacitor component.

Internal Short-Circuit

Touching of the positive and negative plates within a cell.


The time period until a cell/battery loses its expected characteristics.


Also known as electromotive force (EMF), the load draws energy from the battery. Internal battery resistance and depleting state-of-charge cause the voltage to drop.

Low Maintenance

Low maintenance means that no watering nor equalizing charge is required in operating batteries.

Low-Voltage Cut-Off

A circuitry designed to discontinue discharge of a battery at a predetermined voltage level.

Male Tab

The metallic pieces which are attached to a SLA battery as the terminals.

Memory Effect

A phenomenon where a temporary drop of discharge voltage is observed during deep discharge of an alkaline rechargeable battery which has been subjected to shallow charge/discharge. Cycles or trickle charging over long time.

Negative Plate

The battery electrode into which a current from the external circuit flows during discharging. The negative plate has lower electric potential than the positive plate to the electrolyte. The negative plate is incorporated with connection parts such as the electrode pole.

Rated Capacity

A nominal value of capacity of a cell/battery, which is a measure of electric capability. Rated capacity is rather approximate compared with rated capacity.

Nominal Voltage

A nominal value to indicate the voltage of a cell battery. Generally, nominal voltage value of a battery is somewhat lower than its electromotive force. Nominal voltage of the lead-acid battery is 2.0V per unit cell.

Open Circuit Voltage

Measured voltage of a cell/battery which is electrically disconnected from the external circuit.


Continued charging of a fully charged cell/battery. With batteries which require watering, overcharge causes electrolysis of water, resulting in rapid decrease of electrolyte. Generally, overcharge adversely influences battery life.


Discharge of a battery to a voltage below a predetermined cut-off voltage.

Parallel Charge

Simultaneous charging of two or more batteries connected in parallel. In cyclic use of batteries, specifically, the parallel charge tends to cause an imbalance in charge state among the batteries, which may shorten their service life.

Polypropylene Resin

A plastic material which is often used for the case and cover of batteries.

Positive Plate

The battery electrode from which a current flows to the external circuit during discharging. The positive plate has higher electric potential than the negative plate to the electrolyte. The positive plate is incorporated with connection parts such as the electrode pole.

Quick Charge (Rapid Charge)

Charging in a short time with a large current.

Rated Capacity

The stated capacity of a battery; namely, the ampere-hour amount which can be drawn from the battery in fully charged state at a specified temperature, at a specified discharge rate, and to a specified cutoff voltage. The symbol CN may be used to express the rated capacity of N-hour rate.

Rechargeable Battery

The rechargeable battery is a system comprising two different electrodes and an ion-conductive medium, which is capable of converting chemical energy to electric energy, and vice versa. It is also called a secondary battery.

Refresh Charge (Auxiliary Charge)

Charging of a battery mainly to compensate for its self discharge.

Residual Capacity

Residual capacity of a battery after partial discharge or after storage for long time.

Retainer Type

A method to control flowing electrolyte in a battery with the retainer mat, etc...

Reverse Charge

Charging of a battery with its polarity reversed. Namely, the battery discharges.

Self Discharge

Reduction in capacity of a battery while no current is drawn by the external circuit. Self discharge depends on temperature: amount of discharge approximately doubles by each (10°C) rise of ambient temperature.


Voltage describes the nominal open circuit voltage (OCV), which varies with chemistry and number of cells connected in series. Always observe the correct voltage when connecting to a load or a charger. Do not proceed if the voltage does not agree.

Valve Regulated Lead-Acid Battery (VRLA-Battery)

Valve regulated lead-acid battery.


A porous or microporous liquid-absorbent material which is installed between the battery electrodes for preventing short-circuit, securing the separation of the electrodes and retaining electrolyte. The separator should be resistant to oxidation and chemicals; it should excel in electric insulation and liquid-retention; and it should not disturb diffusion of the electrolyte and ionic conduction.

Specific Energy Density

Specific energy or gravimetric energy density defines the battery capacity in weight (Wh/kg); energy density or volumetric energy density is given in size (Wh/l). A battery can have a high specific energy but poor specific power (load capability), as is the case in an alkaline battery. Alternatively, a battery may have a low specific energy but can deliver high specific power, as is possible with the supercapacitor. Specific energy is synonymous with battery capacity and runtime.

Specific Power

Specific power or gravimetric power density indicates the loading capability, or the amount of current the battery can provide. Batteries for power tools exhibit high specific power but have reduced specific energy (capacity). Specific power is synonymous with low internal resistance and the delivery of power.

Standby Use

General term of constant stand-by battery systems. Batteries are kept charged by trickle/float method at all times in preparation for unforeseen power disruptions.

Temperature Compensation

Compensation of charge voltage for temperature variation of a cell/battery or in its vicinity. Qualitatively, charge voltage should be corrected to higher side for low temperatures and to lower side for high temperatures.

Terminal Voltageat Discharge

The voltage of a battery during discharging.

Thermal Runaway

Such phenomena as an excessively high set-up voltage in constantvoltage charging of a battery and a very high battery temperature cause charge current to increase, which then raises the temperature further: this vicious cycle is called thermal runaway, which may, in the worst case, result in breakage of the battery due to heat.

Trickle Charge

To charge a battery in the state of disconnection from the load to compensate for its self discharge.

Trickle Life

The service life of a battery in the trickle use. Usually, the trickle life is the time expressed in years before the dischargeable time of the battery decreases to a half of the initial value.


Abbreviation of Underwriters Laboratories Inc. in USA. The UL establishes various safety standards, and performs official recognition of materials, parts and products.

UPS (Uninterruptible Power Supply)

Equipment or system which is automatically connected to the load to supply power if the main power fails.


A valve on each battery which automatically releases gas from the battery when internal pressure of the battery exceeds a predetermined value: it prevents breakage of the battery due to excessive internal pressure caused by the gas generated by charging or other reasons. The valve also serves to prevent outside air from entering batteries.

Watts and Volt-Amps (VA)

Power drawn from a battery is expressed in watts (W) or volt-amps (VA). Watt is the real power that is being metered; VA is the apparent power that determines the wiring sizing and the circuit breakers. On a purely resistive load, watt and VA readings are alike; a reactive load such as an inductive motor or florescent light causes a drop in the power factor (pf) from the ideal one (1) to 0.7 or lower. For example, a pf of 0.7 has a power efficiency of 70.

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