Active material – In the positive plates, t he active material is lead dioxide. In the negative, it’s metallic sponge lead. When a circuit is created, these materials react with sulfuric acid during charging and discharging. Ampere (Amp) – A unit of measurement for the electron flow or current through a a circuit. Ampere-hour (Amp. Hr., AH) – A unit of measure for a battery’s electrical storage capacity, calculated by multiplying the current in amperes by the time in hours. (Example: A battery which delivers 5 amps for 20 hours provides 5 amps x 20 hours = 100 AH of capacity.) Capacity rating – The time in minutes that a new, fully charged battery will deliver 25 amperes or 75 amperes at 80ºF and maintain a terminal voltage equal to or greater than 1.75 volts per cell. CA – Cranking Amps, 32° CCA – Cold Cranking Amps, 0° (recommended) 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. (Example: A 12-volt battery has 6 cells.) 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. Cycle – One discharge of a battery plus one recharge. Depth of discharge (DOD) – The percentage of capacity actually removed from a battery compared to the total rated capacity. Electrolyte – In a deep cycle battery, it is a dilute solution of sulfuric acid and water. Equalization – An overcharge performed on flooded lead-acid batteries after they have been fully charged. This maintenance step helps eliminate stratification and sulfation. Hydrometer – A tool used to measure the specific gravity of the electrolyte solution. MCA – Marine Cranking Amps, 70° Ohm (Ω) – A unit of measurement for electrical resistance within a circuit. Open circuit voltage – The voltage of a battery when there is no load attached (not receiving or delivering energy). This measurement is best taken when the battery has been at rest for at least 6 hours. 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.) RC – Reserve capacity, 25 amps of discharge (recommended) 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 (S.G.) – A measurement of the strength of battery electrolyte by comparing its density to that of pure water. Stratification – A condition where the concentration of acid is greater at the bottom of the battery than the top. Sulfation – The formation of lead sulfate on the positive and negative electrodes. Volt (V) – A unit of measurement for electrical potential within a circuit. 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.