Valve Regulated Lead-Acid (VRLA) batteries can degrade due to a variety of mechanisms, including corrosion, hard sulfation, water loss, shedding, and active mass degradation. Hard sulfation can be the dominant aging mechanism for many cells. In this paper, pressure feedback is used to minimize water loss during low current charging designed to break up hard sulfate and recover capacity. A VRLA battery that was cycle tested to failure is used to test the desulfation charging control scheme. One cell of this battery that was diagnosed with sulfation degradation was desulfated for 313 hrs at an average current of 0.2 A. The capacity of the cell was recovered by 41% with minimal water loss, demonstrating the effectiveness of the desulfation charge controller.
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