Did you ever wonder about the meaning of terms used in battery literature? Here, courtesy of Europower Battery Centre is a short glossary of the most widely used marine battery terms.

Active Material – In the positive plates, the active material is lead dioxide. In the negative, it’s metallic sponge lead. When a circuit is created, these materials react with sulphuric acid during charging and discharging.

AGM Battery – This is a totally sealed maintenance-free and leak-proof battery giving high starting performance and deep cycling capability. AGM (Absorbent Glass Mat) batteries absorb the battery acid in the glass fibres and thus binds it in.

Ampere (Amp) – A unit of measurement for the electron flow or current through a circuit.

Ampere–Hour (AH) – This is the unit of measure for a battery’s electrical storage capacity. To determine a battery’s ampere-hours, you multiply amperes by hours of discharge.

Battery Group Size – Spec chart designation identifying battery sizes by the Battery Council International. Standard batteries for marine use are sizes 24 and 27.

Capacity Rating – This time in minutes that a new, fully-charged battery will deliver 25 amperes or 75 amperes at 80° F and maintain a terminal voltage equal to or greater than 1.75 volts per cell.

Cell – The basic current-producing unit in a battery. It consists of a set of positive plates, negative plates, electrolyte, separators and casing. A cell’s nominal voltage is 2 volts.

Circuit – The path followed by a flow of electrons. A closed or short circuit is a complete path. An open circuit has a broken path.

Cold Cranking Amps (CCA) – This is the discharge load in amperes which a new, fully charged 12-volt lead-acid battery at 0-degrees Fahrenheit can continuously deliver for 30 seconds and maintain a terminal voltage of at least 7.20 volts.

Cycle – One discharge of a battery plus one recharge.

Deep Cycle – A battery specifically designed to repeatedly run heavy loads and accessories in boating and marine applications.

Depth of Discharge (DOD) – The percentage of capacity actually removed from a battery compared to the total rated capacity.

Discharging – When a battery is delivering power, it is said to be discharging.

Electrolyte – Another term for battery acid. This is the liquid or gelled solution of water and sulphuric acid in a lead-acid battery. Electrolyte conducts and participates in the electrochemical reaction within the battery. In a fully charged lead-acid battery, the typical weight proportion of the elctrolyte is 35 % sulphuric acid and 65% water.

Element – In a battery, a set of positive and negative plates assembled with separators.

Equalisation – An overcharge performed on flooded/wet lead-acid batteries after they have been fully charged. This maintenance step helps eliminate stratification and sulfation.

Flame Arrester– A device located within the degassing system that protects against the risk of gas combustion within the battery there for eliminating the risk of explosion.

Gassing – Gassing occurs when a 12-volt lead-acid battery is charged above 13.8 volts, causing the water to decompose into hydrogen and oxygen gasses. The amount of gassing depends on the portion of the charge current that is not absorbed by the battery and the on-charge potential of the battery.

Gel Batteries – Gel batteries are sealed to guarantee a leak-proof battery in any position. The battery utilises an electrolyte suspension system consisting of high porosity glass fibre material which in conjunction with plates, totally absorbs and contains the electrolyte.

Gelled Electrolyte – This is a jelly-like electrolyte mixture of sulphuric and phosphoric acids, fumed silica and pure water. Gelled electrolyte is used in some marine and wheelchair batteries because it won’t spill. Factory sealed batteries with gelled electrolyte, called Gel-Cell batteries, can provide power even if fully submerged in water or turned upside down.

Hydrometer – This is a device with a float used to measure specific gravity of the liquid electrolyte in a lead-acid battery.

Load Tester – An instrument which measures the battery voltage with an electrical load on the battery to determine its overall condition and its ability to perform under actual engine starting conditions.

Ohm – A unit of measurement for electrical resistance within a circuit.

Open Circuit Voltage – This is the electrical potential of a battery at rest, when it is neither delivering nor receiving power. This measurement is best taken when the battery has been at rest for at least 6 hours. It is typically 12.67 volts for a fully charged lead-acid battery.

Power Inverter – An electronic device that converts direct current (DC) power from a battery into standard alternating current (AC) house power.

Primary Battery – An energy storage device that can deliver energy but cannot be recharged. (i..e. disposable flashlight battery)

Rated (20 Hour) Capacity (AH) – The conventional means for declaring the capacity of a lead-acid battery. It is the ampere-hours that should be delivered by a new, fully charged 12 volt lead-acid battery at 80 degrees Fahrenheit during a continuous 20-hour discharge period and maintain a terminal voltage of at least 10.50 volts.

Reserve Capacity (RC) – The number of minutes which a new, fully charged 12-volt lead-acid battery at 80 degrees Fahrenheit can be continuously discharged at 25 amperes and maintain a terminal voltage of at least 10.50 volts.

Secondary Battery – An energy storage device that can deliver energy and can be recharged. (i..e. automotive or deep cycle battery)

Separator – A divider made of porous material that is placed between the positive and negative plates in a battery cell and allows current to flow through it while preventing direct contact between the plates which would cause a short circuit.

Specific Gravity – This is the density of the electrolyte compared to water. Typically, the electrolyte in a fully-charged lead-acid battery is 1.265 times denser that water at 80-degrees Fahrenheit (27 degrees Celsius).

Stratification – A condition where the concentration of acid is greater at the bottom of the battery than at the top.

Sulfation – The formation of lead sulfate on the positive and negative electrodes.

Volt (V) – A unit of measurement for electrical power.

Watt (W) – A unit of measurement for electrical power.

Watt Hour (WH) – A unit of measurement for electrical power for a certain period of time.