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Find your way through all the technospeak with this handy Glossary of Terms

Word Description / Definition
Acid Liquid in the electrolyte of a lead-acid battery.
Acid Stratification When charging a traditional/flooded lead-acid cell, high-density acid is produced in the plates. This heavy acid drops as a result of gravitation to the lower part of the cell while lower density acid rises to the top of the cell. This stratification of acid can cause loss of capacity and/or battery failure. Acid stratification is a much smaller concern in AGM batteries.
Active Material

Chemically active compounds in a cell or battery that convert from one composition to another while producing current (electrical energy) or accepting current from an external circuit.

Absorbent Glass Mat (AGM)

The mat of microglass fibers which is used for fixing the sulfuric acid in lead accumulators.

Ampere (Amp)

The unit of measure of the electron flow, or current, through a circuit.

Ampere (Amp) Hours

The unit of measure for a battery’s electrical storage capacity. Multiply the current in amperes by the time in hours of discharge.


One or more galvanic (electrochemical) cells electrically coupled into a single unit and equipped with attachments for external electrical connections.

Battery Charger

Device supplying electrical energy to a secondary battery.


The ability of a fully charged battery to deliver a specified quantity of electricity at a given rate over a definite period of time.


The basic electrochemical current-producing unit in a battery consisting of a set of positive plates, negative plates, electrolyte, separators and casing. There are six cells in a 12-volt lead-acid battery.

Charge Acceptance

The quantity of current in ampere hours which a battery in a defined charge state can accept at a specified temperature and charge voltage within a defined period.

Circuit Path followed by a flow of electrons. A closed circuit is a complete path. An open circuit has a broken or disconnected path.
Cold Cranking Amps (CCA) Number of amperes a lead-acid battery at 0oF (-17.8oC) can deliver for 30 seconds and maintain at least 1.2 Volts per cell.
Container The polypropylene or hard rubber case which holds the plates, straps and electrolyte.
Corrosion Destructive chemical reaction of a liquid electrolyte with a reactive.
Cover  The lid for the container.
Current Flow of electricity measured in amperes.
Cycle Charging followed by discharging, repeated at regular intervals.
Deep-Cycle Battery Battery that provides a steady amount of current over a long period of time, provides a surge when needed and designed to be deeply discharged over and over again.
Discharge Delivering current through the battery.
Deep Discharge State in which a cell is fully discharged using low current, so that the voltage falls below the final discharging voltage.
Electrolyte A solution of sulfuric acid and distilled water which conducts current through the movement of ions between positive and negative plates.
Grid Lead alloy framework that supports the active material of a battery plate and conducts current.
Ground Reference potential of a circuit. In automobile use, the result of attaching the battery cable to the body frame which is used as a path for completing a circuit in lieu of a direct wire from a component. Today, over 99% of autos use the negative terminal of the battery as the ground.
Lead Acid Battery Battery made up of plates, lead, and lead oxide (various other elements are used to change density, hardness, porosity, etc.) with a 35 percent sulfuric acid and 65 percent water solution. This solution is called electrolyte, which causes a chemical reaction that produce electrons.
Maintenance-Free Battery Battery in which you don't have to check or refill the electrolyte levels.
Ohm Unit for measuring electrical resistance or impedance within an electrical circuit.
Plate - Positive Cast metallic frame which contains the lead dioxide active material.
Plate - Negative Cast metallic frame which contains a spongy lead active material.
Reserve Capacity Rating (RC) Number of minutes a battery at 26.7o C/80o F can be discharged at a 25-amp rate until reaching a voltage of 10.5 volts (for a 12 volt battery) and maintain a voltage at 10.5 volts for a 12 Volt battery. The higher the rating, the longer your vehicle can operate should your alternator or fan belt malfunction.
Sealed Battery Battery in which you don't have to check or refill the electrolyte levels. Leak proof at angles over 45 degrees, also called VRLA (Valve Regulated Lead-Acid).
Separator Porous dividers between plates that prevent physical contact between plates.
Short Circuit An unintended current-bypass in an electric device or wiring, generally very low in resistance and thus causing a large current to flow. In a battery, a cell short circuit may be permanent enough to discharge the cell and render the battery useless.
Starting, Lighting, Ignition (SLI) Battery Rechargeable battery that supplies electric energy to an automobile to power the starter motor, the lights, and the ignition system of a vehicle’s engine.
State of Charge (SOC) The amount of electrical energy stored in a battery at a given time expressed as a percentage of the energy when fully charged.
Terminals Electrical connection from the battery to the external circuit. Each terminal is connected to either the first (positive) or last (negative) strap in the series connection of cells in a battery.
Valve Regulated Lead-Acid (VRLA) Battery Battery which is sealed and maintenance free.
Volt Unit of measure for electrical potential.
Watt Unit of measure for electrical power.
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