Abstract: Disclosed are a heat-generating device for a battery and a battery assembly enabling a battery to stably produce electricity even under low-temperature conditions. The heat-generating device for a battery includes a heating element positioned on one side of the battery and generates heat through a reaction with the air. The heating element comprises a main body generating heat through the reaction with the air, and a supporting body wrapping the main body to adhere to the battery. Accordingly, the internal temperature of the battery can be maintained within possible activation temperature ranges to allow the battery to produce electricity, thereby making the battery performance sustainable under low-temperature conditions.