Using an industrial lithium-ion battery that has higher energy density than conventional valve-regulated lead-acid batteries, a rack-mounted DC-power-supply system was assembled and tested at a base transceiver station (BTS) during actual service. The nominal output voltage of the system is 53.5 V and the maximum output current is 20 A. An 80-Ah lithium-ion battery composed of 13 cells connected in series was used and maintained by the floating charge method. The DC-power-supply system was installed in a 19-inch power rack in the telecommunications equipment box at the BTS. The characteristics of the 80-Ah lithium-ion battery, specifications of the DC-power-supply system and field-test results are presented here.