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Batteries should be tested at regular intervals to (a) determine whether the battery meets its specification or the manufacturer's rating, or both; (b) periodically determine whether the performance of the battery, as found, is within acceptable limits, and (c) if required, determine whether the battery as found meets the design requirements of the system to which it is connected. The schedule and procedure for battery capacity tests should be performed according to the requirements of ANSUIEEE Std 450, IEEE Recommended Practice for Maintenance, Testing, and Replacement of Large Lead Storage Batteries for Generating Stations and Substations.. For an acceptance or performance test, use the following equation to determine battery capacity:
where
ANSI/IEEE Std 450 recommends replacement of a battery if its capacity as determined from the equation above is less than 80% manufacturer's rating. A capacity of 80% shows that the battery rate of deterioration is increasing even if there is ample capacity to meet load requirements. If individual cells are required to be replaced, they should be compatible with existing cells and tested prior to installation. It is recommended that when one or more cells/jars are replaced the entire battery string be replaced in order to prevent large differences in cell impedance. If uncorrected, this may result in unequal charging of the battery string. STORAGE, TRANSPORTATION, AND DISPOSAL Storage The storage of lead-acid batteries is fairly straightforward. Lead-acid batteries must be stored in the open-circuit condition with the terminals insulated. Long periods of storage at even low drain rates may result in permanent damage. Batteries should be stored in cool, dry, environments in their upright position. To maximize the length a battery may be stored it should be completely charged in the beginning. Batteries that will be stored for extended periods should undergo regular open-cell voltage (OCV) checks and be recharged as necessary or at regularly scheduled intervals. An important consideration during storage is a damaging process called sulfation. As cells sit in storage and self-discharge, the active materials of the electrodes convert to lead sulfate just as they do in other discharges. But, in self discharge the lead sulfate forms as larger crystals that have the effect of insulating the particles of the active material, either from each other or the grid. Since lead sulfate occupies more space than sponge lead, the negative plate expands in volume. If the cell is allowed to overdischarge, the lead sulfate may expand to the point where it separates from the sponge lead and falls to the bottom of the jar as sediment. The overall effect is a loss of capacity and greater internal resistance. Sulfation is normally reversible for lead sulfate still attached to the negative plate by charging with a low current until the lead sulfate is converted back into sponge lead.
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