A DC backup power supply system having a battery; a charge-discharge circuit for charging and discharging a power between the battery and a DC line; and a control circuit for controlling the charge-discharge circuit, wherein the battery has a number of battery cells and cylindrical portions of the battery...http://www.google.com/patents/US20030222618?utm_source=gb-gplus-sharePatent US20030222618 - DC backup power supply system
