NOVELTY - The apparatus has a battery (4) for supplying electric power to an electric motor or power-generation motor (6), when an electric generator or motor generator (2) charges the battery. A heat exchanger i.e. heater core (12a), is arranged on a refrigeration circuit. A battery temperature sensor (4a) detects temperature of the battery. A controller (15) operates a switching valve i.e. three-way valve (13), on basis of temperature of the battery and allows a temperature medium i.e. cooling water, to flow through a battery-heating channel i.e. heat branch (8b).    USE - Apparatus for warming up a battery e.g. lithium-ion battery, lead storage battery, nickel-cadmium battery, air battery and sodium-sulfur battery, for a vehicle i.e. front-wheel drive hybrid vehicle. Can also be used for a rear-wheel drive vehicle and a four-wheel drive vehicle.    ADVANTAGE - The heater core for a cabin heater is provided on the heat branch, and inside of a vehicle cabin is heated by using heat generated by an engine for power generation, so that influence of usage of the cabin heater on cruising range of the vehicle is reduced. The apparatus supplies the coolant fluid to the battery in a case where the temperature of the battery is low after the engine is started, so that the battery is warmed up without increasing consumption of the electric power of the battery, thus reducing load or stress applied to the battery. The engine for driving the power-generation motor is small in size, so that the apparatus is formed in small size and inexpensive.    DETAILED DESCRIPTION - An INDEPENDENT CALIM is also included for a method for warming up a battery for a vehicle.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic block diagram of a running system or power train of a hybrid vehicle mounted with a battery warm-up apparatus.    Motor generator (2)    Battery (4)    Battery temperature sensor (4a)    Power-generation motor (6)    Heat branch (8b)    Heater core (12a)    Three-way valves (13, 14)    Controller (15)