A system for managing a battery of a vehicle may include: a temperature sensor measuring temperature of external air; an electric device cooler including an electric device mounted in the vehicle, an electric device cooling pipe through which cooling water for cooling the electric device flows, and a first pump circulating the cooling water; a battery cooler including a battery and a battery cooling pipe through which the cooling water for cooling the battery flows; one or more 3-way valves connecting or disconnecting the electric device cooling pipe to or from the battery cooling pipe; and a controller configured to control the first pump and the one or more 3-way valves to move the cooling water in the battery cooling pipe to the electric device cooling pipe when the measured temperature of the external air is the predetermined temperature or less.