Days in storage at 25- CLead-calcium gridLead-Acid Storage BatteriesDOE-HDBK-1084-95OPERATON AND CONSTRUCTIONRev. 0Page 17BatteriesFigure 7. Self-discharge rates of three grid materials.by long-term overcharging, which is common to UPS and other batterieson constant-float changing. Grids may grow in size sufficiently to causebuckling or rupture of their containers.Another type of grid alloy is lead-selenium. In reality, this battery is actually a lowlead-antimony grid with a slight amount of selenium. Lead-selenium has characteristicsthat fall somewhere between lead-calcium and lead-antimony.When pure lead is mixed with an alloy there may be undesirable characteristicsintroduced in the performance of the battery. Modern day battery manufacturers try toreduce the amount of antimony and calcium by introducing doping agents such asselenium, cadmium, tin, and arsenic. When batteries containing arsenic and antimonyare charged (especially overcharged) the poisonous gases arsine (AsH ) and stibine3(SbH ) may be released. This is discussed further in the paragraphs devoted to3charging.SpecificGravityOne of the key parameters of battery operation is the specific gravity of the electrolyte. Specific gravity is the ratio of the weight of a solution to the weight of an equal volume ofwater at a specified temperature. Specific gravity is used as an indicator of the state of chargeof a cell or battery. However, specific gravity measurements cannot determine a battery'scapacity. During discharge, the specific gravity decreases linearly with the ampere-hoursdischarged as indicated in Figure 8.
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