Load Test Accuracy Issues

Are Load Tests Accurate Capacity Benchmarks?

Repeatability and Other Unavoidable Issues

BATTERY - EKG typically provides results that agree within seven percent of a load test determination of string capacity, ten percent for individual cells. Part of this difference comes from the load test itself. A measurement cannot be more accurate than the benchmark used for comparisons. However, load test capacity determinations normally vary by a few percent among consecutive tests made over a short period of time (several days or months), even under carefully controlled conditions.

Furthermore, older batteries usually show broad capacity distributions among the cells in the string. Since load tests must be terminated when the weakest cells drop below their cutoff voltages, to avoid damage to the battery, the healthiest cells cannot be fully discharged, and the capacities of such cells cannot be determined. This deficiency is not observed by our monitoring system, because the cells are not discharged.