Definitions

Lead-Acid Storage Batteries DOE-HDBK-1084-95 DEFINITIONS Rev. 0 Page 3 Batteries Float charge - Method of charging in which a secondary cell is continuously connected to a constant-voltage supply that maintains the cell in a fully charged condition. Gassing - Evolution of gas from one or more electrodes resulting from electrolysis of water during charge or from self-discharge. Significant gassing occurs when the battery is nearing the fully charged state while recharging or when the battery is on equalizing charge. Potential difference - Work which must be done against electrical forces to move a unit charge from one point to the other, also known as electromotive force (EMF). Primary cell or battery - Cell or battery which is not intended to be recharged and is discarded when the cell or battery has delivered its useful capacity. Secondary battery - A battery that after discharge may be restored to its charged state by passage of an electrical current through the cell in the opposite direction to that of discharge. (Also called storage or rechargeable.) Separator - Electrically insulating layer of material which physically separates electrodes of opposite polarity. Separators must be permeable to ions in the electrolyte and may also have the function of storing or immobilizing the electrolyte. Specific gravity - Ratio of the weight of a solution to an equal volume of water at a specified temperature. Used as an indicator of the state of charge of a cell or battery. Sulfation - Formation of lead sulfate crystals on the plates of a lead-acid battery. Terminal - External electric connections of a cell or battery, also referred to as "terminal post" or "post." Thermal runaway - A condition that occurs in a battery (especially valve-regulated types) when charging energy results in heat generation within the battery greater than the heat dissipated, causing an uncontrolled rise in battery temperature. This can cause failure through cell dry-out, shortened life, and/or melting of the battery.