Long-life nickel-metal hydride batteries as a backup power supply for optical fiber networks

The authors have developed a nickel-metal hydride (Ni/MH) battery that has a lifetime of eight years at 30/spl deg/C and operates at temperatures from -10/spl deg/C to 55/spl deg/C. This performance was achieved by improving the Ni/MH cells and optimizing their charging. Optimizing the metal-hydride and electrolyte contents of the Ni/MH cells extended cell lifetime from one to two years. Use of an intermittent current-pulse charging method that inhibits cell degradation due to overcharging extended cell lifetime to three times that of cells charged using trickle-charging. Use of an optimum intermittent charging condition allows four batteries to be charged sufficiently at the current needed to fully charge only one battery. This battery has been used as the backup power source in optical network units (ONUs) of Fiber-To-The-Home (FTTH) networks and in the HUB power supplies of Fiber-To-The-Pole (FTTP) networks.