Practical Model-Based Methodologies to Determine the State of Charge of Li/CFx Batteries

In the realm of primary cells, the Li/CFx chemistry holds immense potential due to its unmatched theoretical specific energy, longevity, and shelf time. However, little work has been done on creating a simple, practical methodology to determine the state of charge (SoC) of a partially-discharged battery in critical applications, such as remote sensing and probing, and mission control hardware. We propose an approach in which the SoC can be estimated by measuring the output voltage under various current loads and fitting the data to an original model in the general form of a logistic curve. The resulting function can then be used in conjunction with least squares analysis to efficiently estimate the SoC.