In this research, a first order polynomial and a first order Gaussian function are combined to describe the discharge behavior of a Lithium-ion cell battery. The first order polynomial is used to describe the middle part of the discharge curve, and the first order Gaussian is to fit the final part of the curve. As a result, in the curve of percentage of remain capacity versus voltage, the major difference between the observed discharge curve and the curve generated from our model happens only in the beginning of the discharge. In the middle and the later part of the discharging, our model fits very well to the observed discharge curve. The differences are well within 0.1 volts. As to the percentage of remaining capacity, the differences are within 2 percents. To the users, the important concern is how much the capacity remains to be used, rather than how much capacity they have used. Thus, the understanding of the later part of the discharge curve is much more important than that of the earlier part. In our model, it takes only 5 parameters to describe the behavior of discharge in each case. Therefore, we believe that we have developed a simple, yet accurate model to describe the discharge behavior of a lithium-ion battery.
