• A type of chemical that can release hydrogen ions when mixed with water. Sulfuric acid is used in a lead-acid battery.

Ampere (Amp, A)

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

Ampere-Hour (Amp-Hrs, Ah)

  • A unit of measure for a battery’s electrical storage capacity, obtained by multiplying the current in amperes by the time in hours of discharge. (Example: A battery that delivers 5 amperes for 20 hours delivers 5 amperes x 20 hours = 100 amp-hrs of capacity.)


  • Cold Cranking Amps is a rating used in the battery industry to define a battery’s ability to start an engine in cold temperatures. A great amount of amperes is needed to start the engine, but only for a short time.The actual rating is the number of amps that can be removed from a new fully charged battery at 0°F for 30 seconds while maintaining a voltage of at least 7.2 volts (for a 12-volt battery).As a battery ages with use, it may no longer be able to meet its original CCA rating.The higher the CCA rating, the greater the starting power of the battery.

Deep-Cycle Battery

  • Battery that provides a steady amount of current over a long period of time, provides a surge when needed and is designed to be deeply discharged over and over again.

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. (Largely referred to as car battery).


    • In a lead-acid battery, the electrolyte is sulfuric acid diluted with water. It is a conductor that supplies water and sulfate for the electrochemical reaction: PbO2 + Pb + 2H2SO4 = 2PbSO4 + 2H2O.


    • Electrolyte that has been immobilized by the addition of a chemical agent, normally fine silica, to prevent spillage. Batteries made with gelled electrolyte are often referred to as gel batteries. Gel batteries are one typical type of VRLA battery.

    Reserve Capacity Rating

    • The time in minutes that a new, fully charged battery will deliver 25 amperes at 27°C (80°F) 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.

      Electronic Tester

      • An electronic device that assesses the condition of a battery through an ohmic measurement such as resistance or conductance, typically without drawing large current loads.


      • A device used to measure the strength (i.e., the concentration of sulfuric acid in the electrolyte) of the electrolyte through specific gravity of the electrolyte.

      Specific Gravity (Sp. Gr. or SG)

      • Specific gravity is a measure of the electrolyte concentration in a battery. This measurement is based on the density of the electrolyte compared to the density of water and is typically determined by the use of a hydrometer (see Hydrometer). By definition, the specific gravity of water is 1.00 and the specific gravity of the sulfuric acid electrolyte in a typical fully charged battery is 1.265-1.285. Specific gravity measurements are typically used to determine if the battery is fully charged or if the battery has a bad cell.

        Load Tester

        • An instrument that draws current (discharges) from a battery using an electrical load while measuring voltage. It determines the battery’s ability to perform under actual discharge conditions.


        • An electronic device used to measure voltage, normally in a digital format.


        • Valve-regulated lead-acid battery. AGM and gel are the two types of VRLA batteries. These batteries have no “free” liquid electrolyte and in the cell operate on the oxygen recombination cycle, which is designed to minimize water loss. VRLA batteries feature vents that are one-way burp valves. These low-pressure burp valves prohibit air ingress to the cell while permitting gases to vent from the cell if necessary. The pressure maintained in the battery, though only very slight (<3-psi) is required to facilitate the oxygen generated at the positive plates back into water.

          MCA (Marine)

          • MCA is an industry rating defining a marine battery’s ability to deliver a large amount of amperage for a short period of time. Since marine batteries are typically never used at temperatures below freezing, marine cranking amps are measured at 32°F as opposed to 0°F for cold cranking amps. The rating is the number of amps that can be removed from a marine battery at 32°F for 30 seconds while maintaining a voltage of at least 7.2 volts for a 12-volt battery. The higher the MCA rating, the greater the starting power of the marine battery.

            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 produces electrons.


            • Designating, or pertaining to, a kind of electrical potential; opposite of negative. A point or terminal on a battery having higher relative electrical potential. The positive battery terminal is the point to which electrons flow during discharge.


            • Designating, or pertaining to, electrical potential. The negative battery terminal is the point from which electrons flow during discharge.