VRLA Battery failures are frequently encountered during the production of Uninterruptible Power Supplies (UPS). This paper presents two simple techniques for evaluating failed batteries. The first method comprises of plotting constant current discharge characteristics (CCD) at load levels encountered in UPS application. CCD curves of several freshly charged good batteries are first generated to be used as standard curves. CCD curves obtained form defective or failed batteries are then compared to CCD curves of the standard. In the second method we plot the variation of loaded voltage (V) as a function of load current (I). Standard I-V curves are generated for good batteries in known state of charge (SOC) ranging from 100precent to 50precent. The depth of discharge (DOD) resulting from this test is ensured to be less than 5precent. Curves obtained from defective or failed batteries can then be compared to the standard I-V curves. The paper discusses the theoretical, mathematical and experimental aspects of these two methods. Both of these methods can be easily implemented in-house before proceeding to destructive tests at a failure analysis laboratory, should such tests be found necessary. Several results obtained are presented, along with the limitations of the methods.
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