Battery Basics

A handy guide to the technical terms used in the battery market today
To help you understand many of the technical jargon relating to battery construction and performance, we've put together the guide below that explains what many of the most commonly used terms mean.
Absorbent Glass Mat (AGM)

A battery constructed with an absorbed glass mat does not contain any free liquid electrolyte. The electrolyte is absorbed in a glass mat material located in each of the battery’s cells. AGM batteries are ideal for vehicles with automatic start-stop systems with braking energy recovery (recuperation), or for cars with premium equipment and sophisticated accessories. They are a higher tier option to the EFB battery.

Ampere (amp or 'A')

The unit of measure of current through a circuit- named after the French mathematician André-Marie Ampère, hence the capitalisation of the 'A'.

Amp Hour (Ah)

A unit of measurement of a battery’s electrical storage capacity. It is calculated by multiplying the current (amps) by the length of time of discharge in hours, so a battery that delivers 5 amps for 20 hours is said to have 100Ah capacity (5A x 20hrs).


The ability of a fully charged battery to deliver a specified quantity of electricity (Ah) at a given rate (A) over a definite period of time (hrs). The capacity of a battery depends on a number of factors such as: active material weight, density of the active material, number, design and dimensions of the plates, plate spacing, design of separators, electrolyte quality, rate of electrical discharge, temperature, age, and life history of the battery.


The cell is the basic current-producing unit in a battery, consisting of a set of positive and negative plates, electrolyte, separators and a casing. There are six cells to a 12V lead acid battery, each having a voltage of approx. 2.2V, which gives a normal 12V lead acid battery it's 13.2V reading.

Charging Rate

The current (amps) at which a battery is charged.

Cold Crank Amps (CCA)

The number of amps a lead acid battery can deliver for 30 seconds at a temperature of -17.8 Deg C and maintain at least 1.2 volts per cell.


The rate of flow of electricity along a conductor. It is comparable to the flow of a stream of water. The SI unit of measure for current is the ampere (A). A battery delivers direct current (DC).


One discharge plus one recharge equals one cycle.

Deep Cycle

The deep cycle battery is built to provide continuous power for leisure uses such as caravans and motor homes. They are also used in marine applications, often alongside a starter battery. It is built for maximum capacity and a reasonably high cycle count, which is achieved by making the lead plates thick.


The electrolyte in a lead-acid battery is, in it's simplest form, sulphuric acid diluted with distilled water. Modern electrolytes can be quite complex and contain soluble salts and other bases, and can exist in liquid and gel formats. Electrolyte is electrically conductive and supports the electro-chemical reaction (flow of ions) that provides the current or receives the re-charge.

EFB / AFB / ECM Technonlgies

EFB (Enhanced Flooded Battery) / AFB (Advanced Flooded Battery) / ECM (Enhanced-Cycling-Mat) are all terms used for the same type of battery.

The most common term is EFB- these batteries were introduced as a lower tier option to AGM batteries in terms of performance and durability. They are an enhanced version of standard wet-flooded technology and were developed for the vehicle Stop-Start market.


Normally a lead alloy framework know as a plate, which conducts current. Pure lead is too soft and would not support itself, so small quantities of other metals are added to get the mechanical strength and improve electrical properties.

Reserve Capacity (RC)

The time in minutes that a new, fully charged, battery will deliver 25 amps at 26 Deg C and maintain a terminal voltage equal to, or higher than, 1.75 volts per cell. This rating represents the time the battery will continue to operate essential accessories if the alternator or generator of a vehicle fails.


A divider between the positive and negative plates of an element which allows the flow of current to pass through it. Separators are made from numerous materials, such as polyethylene, polyvinyl chloride, rubber, glass fibre, cellulose, etc.

State of Charge (SOC)

This is a measurement of the amount of energy available in a battery at a specific point in time, normally expressed as a percentage. It generally represents the short term capability of the battery.

State of Health (SOH)

This is a measurement that generally reflects the long term capability of the battery to deliver it's rated performance. It takes into account such factors as charge acceptance, internal resistance, voltage and self-discharge

Voltage (V)

The Volt is the SI unit of measure for electric potential difference, named after the Italian physicist Alessandro Volta, hence the capitalisation of the 'V'.

Voltage is the difference in electrical potential that exists between the terminals of a battery, or any two points in an electrical circuit.

Its relationship to current is described as V=I x R, which is known as Ohm's Law, where I = current (measured in amps) and R =resistance (measured in ohms),

Valve Regulated Lead Acid (VRLA) Battery

A sealed battery that features a safety valve designed to release excessive internal pressure while maintaining sufficient pressure for recombination of oxygen and hydrogen into water. VRLA and AGM typically refer to the same type of battery design.


The Watt is the SI unit of measure for electrical power, named after James Watt, an 18th-century Scottish inventor, hence the capitalisation of the 'W'.

Power (watts) = I (amps) x V (volts)

A kWh is a measure of energy, which is power used or generated, multiplied by a duration