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Voltage-Slope Method Reserve Time Accuracy

Dave Essi

Aspects of a simple algorithm for computing reserve time during discharge were discussed in the 2018 Battcon paper “Time (Only) Referenced Rundown Test.” Specifically, the paper presented an example of the voltage-slope technique explained as method 1 in US Patent 6,211,654 by Thomas D. O’Sullivan. This follow-up paper examines the accuracy of these predictions made using the voltage-slope technique. Predictions and actual results are compared using discharge data supplied by a battery manufacturer. Predictions against battery curve table estimates are also examined. In addition, the paper examines how the method 2 division factors effect of the accuracy of the result (e.g. an End Voltage of 1.75 VDC requires a division factor of 2). Variables such as depth of discharge and slope-width (time duration) will also be considered. Lastly, this paper demonstrates how the method 3 calibration works and improves predictions.

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