Glossary of Battery Terms

Active Material:
The porous structure of the lead compounds that produce and store the electrical energy within a lead-acid battery.

AGM (Absorbed Glass Mat):
A type of separator material that is comprised of glass microfibers that absorbs and retains the electrolyte leaving no free liquid in the cells to spill. Batteries made with this battery separator are called AGM Batteries and classified under the VRLA

A unit of measurement for electrical current.

Ampere Hour (AH):
The quantity of electrical energy corresponding to the flow of current of one ampere for one hour. This term is used to signify the energy stored in the battery.

Automotive “Starter” Battery (SLI):
An automotive battery is designed to provide a short burst of high power to crank / start an engine.

Depth of Discharge for a “starter” battery is approximately 5-15% of capacity.

Battery Capacity:
The total number of ampere hours (AH) that a fully charged battery can output.

Boost Charge:
A short time / high current charge process to ensure that the plates of the battery are charged sufficiently to perform desired function.

An electrical pathway followed by flow of electrons. A closed circuit is a completed path whereas an open circuit has a broken or disconnected pathway.

Circuit Series:
A circuit that has only one path for the flow of current.

Please see Serial Connection.

Circuit Parallel:
A circuit that provides more than one path for the flow of current.

Please see Parallel Connection.

Cold Cranking Ampere (CCA):
The ampere that a fully charged battery at -18 degrees Celsius can deliver for 30 seconds and maintain a voltage of 1.2 volts per cell or higher. (7.2 Volts for a 12 volt battery).

The chemical or electrochemical reaction between a material and its environment that produces a deterioration of the material and its properties.

In Lead Acid batteries the positive lead grids gradually corrode during use – often leading to battery failure.

C-rating (C/20, C/10, C/5):
The charge and discharge currents. i.e. a 100ah C/20 battery delivers 5 amperes per hour for 20 hours (100 ÷ 20).

Automotive “starter” batteries capacities are usually expressed at C/10 or C/20, whereas Deep Cycle batteries are expressed at C/10.

One sequence of charge and discharge.

Deep Cycle Battery:
A deep cycle battery is designed to provide a steady continuous current over a long period of time.

These types of batteries are specifically designed for Solar or other applications (golf cart, backup power, etc) that require the battery to be deeply discharged time and again.

Depth of discharge for deep cycle type is around 70-80% of total battery capacity.

Depth of Discharge (DOD):
The available percentage of total battery capacity available for discharge.

Automotive “starter” batteries usually have between 5-15% DOD.

Deep Cycle batteries usually have between 70-80% DOD.


When a battery is delivering a current.

Dry Charged Battery:
Type of battery in which both the positive and negative plates are formed and charged in acid baths before being dried and assembled.

The battery is activated once electrolyte is added, at which time the battery will give instant current and be ready for use.

RB Dry Charged Car Battery

A dilute solution of Sulphuric Acid and Water.

Chemical formula is H2SO4

Equalization Charge:
A supplementary charge utilized to ensure all battery cells are charged equally and that electrolyte is fully mixed by the gas bubbles (gassing).

Floating Charge:
Method of recharge whereby a cell / battery is supplied just enough current to equal the self discharge of the battery, thus ensuring the cell/battery is maintained in a fully charged condition.

Flooded cell type battery:
A form of rechargeable battery in which the battery plates are immersed in liquid electrolyte (battery acid).

A process of charging the battery or battery plates for the first time.

This changes the lead oxide paste of the positive grid into lead dioxide.

For the negative plate it changes from Lead oxide paste to metallic sponge lead.

This process occurs when more current is supplied to a cell / battery than can be absorbed.

Excess current produced Hydrogen and oxygen gas bubbles.

Electrolyte that has been immobilized by the addition of fine silica to avoid spillage.

A lead alloy framework that support the active material of a battery plate and conducts current.

An instrument used to measure that specific gravity of the electrolyte.


Maintenance Free Battery (MF):

Similar to a dry charged battery, however the battery is filled with electrolyte at the factory and ready for use by completion of manufacturing process.

Battery type that require no water servicing during its lifetime of use.


Open Circuit Voltage:
The Voltage of a cell / battery without any load (i.e. not receiving or delivering energy).

Over Charge:
The process of continued charge of cell / battery after the point of 100% charge capacity.

Over Discharge:
The process of discharging a cell / battery beyond its cut off voltage.

Parallel Connection:
The term to describe the connection of multiple batteries with all like terminals (+/+ , -/-) connected together to obtain a higher AH

I.E. Two 12volt / 70ah batteries connected using the parallel method will give a total value of 12volts / 140ah (70ah X 2).

RB Parellel Connection

A thin flat unit that is comprised of the grid and active material.

The plate supports the active material and conducts the electrons out of the cells.

Reserve Capacity (RC):
The number of minutes that a fully charged battery can be discharged at 25ah and maintain a minimum of 1.25 volts per cell.

Sealed Maintenance Free (SMF) Battery:
See Maintenance Free Battery

Secondary Battery:
A battery that can store and deliver electrical energy and can be recharged by passing direct current through it in a direction opposite to that of discharge.

A lead acid battery is a secondary battery.

Self Discharge:
The loss of capacity (discharge) of a battery while it is in an open circuit.

Serial Connection:
The term used to describe the connection of multiple batteries with the Positive (+) terminal of each battery connected to the Negative (-) terminal of the adjacent battery to increase the voltage

I.E. Two 12volt / 70ah batteries connected using the Serial method will give a total value of 24volts / 70ah (12volt X 2).

RB Serial Connection

A divider made of porous material, placed between the Positive (+) and Negative (-) plates, to allow current flow without direct contact between plates as this would cause a short circuit.

Short Circuit:
An unwanted electrical connection between Negative (-) and Positive (+) plates.

A short circuit can damage the battery and any connected equipment as well as causing sparks and or fire.

Specific Gravity (SG):
The density of the electrolyte (battery acid) compared to water.

The Specific Gravity of electrolyte is measured using a Hydrometer.

A fully charged battery SG is 1.265 @ 25 degrees Celsius.

A fully discharged battery SG is 1.12 @ 25 degrees Celsius.

State of Charge:
The amount of deliverable low-rate electrical energy stored in a battery at any given time.

This is expressed as a percentage of the energy when fully charged and measured under the same discharge conditions.

A fully charged battery has a state of charge of 100%

A term used to refer to the lead sulphate crystals that can grow on battery plates due to consistent low state of charge.

Sulfation inhibits current flow and damages the battery.

The structures on the battery that allows the external circuit to be connected.


Mechanisms to allow the gasses produced in a battery to escape while keeping the electrolyte in the battery.

Vents come in both permanently fixed (i.e. in the SMF / MF batteries) as well as removable (dry charged battery) designs.

A unit of measurement of electrical energy within an electrical circuit.

Most batteries come as 6 / 12 or 24 volts with each cell as 2 volts.

VRLA (Valve Regulated Lead Acid) Battery:

VRLA batteries are batteries produced utilizing either the Gel or AGM technology in which the electrolyte of the battery is been suspended as a Gel (Gel Batteries) or absorbed (AGM batteries) so that the electrolyte is no longer free moving.