Development of long-life trickle-charged Ni/Cd cells and cell life evaluation

We have developed long-life trickle-charged nickel-cadmium (Ni/Cd) cells to use as a backup power supply for optical network units when the commercial power supply fails. The cells were estimated to survive for 10 years or longer at 30°C and operate in a temperature range of -20°C to +60°C. We also found an effective method for evaluating cell life. In the test where the cells were charged and discharged in cycles at constant currents and temperature, the capacity decreased almost linearly with the logarithmic cycle number. We could extrapolate the cell life from the plot of the capacities after only a few cycles. Furthermore, we found that the charging duration could be shortened in the test because decrease in capacity as cycle number increased did not depend on the charging duration