able 1. Specific gravities for flooded batteries

Lead-Acid Storage Batteries DOE-HDBK-1084-95 OPERATON AND CONSTRUCTION Rev. 0 Page 19 Batteries volume of electrolyte expands as temperature rises and contracts as temperature drops, therefore affecting the density or specific gravity reading. As the volume of electrolyte expands, the readings are lowered and, conversely, specific gravity increases with colder temperatures. The specific gravity for a given battery is determined by the application it will be used in, taking into account operating temperature and battery life. Typical specific gravities for certain applications are shown in Table 1. Table 1. Specific gravities for flooded batteries. Specific gravities Application 1.300 Heavily cycled batteries such as for electric vehicles (traction) 1.260 Automotive (SLI) 1.250 UPS—Standby with high momentary current discharge requirement 1.215 General applications such as power utility and telephone applications In the selection of a battery for a given application, some of the effects of high or low specific gravity to be considered are: Higher gravity Lower gravity More capacity Less capacity Shorter life Longer life Less space required More space required Higher momentary discharge rates Lower momentary discharge rates Less adaptable to "floating" More adaptable to "floating" operation operation More standing loss Less standing loss A solution of higher specific gravity is heavier per unit volume than one of lower specific gravity. Therefore the more concentrated electrolyte created during charging sinks to the bottom of the battery jar creating a gradient in specific gravity. The gassing that occurs on overcharge serves as a "mixer" and makes the specific gravity uniform throughout the cell. To avoid erroneous readings, specific gravity measurements should only be taken after an equalizing charge and subsequent float charge for at least 72 hours. The reader should seek additional guidance on specific gravity from ANSI/IEEE Std 450, IEEE Recommended Practice for Maintenance, Testing, and Replacement of Large Lead Storage Batteries for