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Experimental Evaluation of the True Remaining Capacity of Legacy Lead-Acid Batteries

One of the common challenges in remote microgrid installations is inexpensive, reliable, and less labor-intensive battery tests to measure the capacity of used batteries and link it to their remaining life. These capacity tests are usually misinterpreted, which results in a healthy battery being junked or may arise economic issues due to oversized battery banks in microgrids. In this work, we conducted several discharge experiments on 12V 100Ah lead-acid batteries in a controlled manner using an electronic load. The battery is subsequently discharged to 10.5V at C2.5, C3, C5, C10, C20, and C40 rates. When summed up using altered C-rate discharge sequences, the individual capacities resulted in 100.71Ah, 100.23Ah and 78.96Ah, 89.43Ah for the fresh and weak batteries, respectively. Irrespective of the discharge sequence, the cumulative net capacities are found quite close to the battery's actual capacity for fresh but much different for weak batteries. Results show that the remaining battery's true capacity does not disappear at a high rate and may further be utilized at lower discharge rates. The outcome of these experiments provides the basis to identify fresh and weak batteries and to size the battery banks for the low-cost rural microgrids more efficiently and economically.