BATTERY PACK AND PTC ELEMENT INCORPORATED IN THE BATTERY PACK

A battery pack and a PTC device are provided that can be used safely under large current loads by increasing the area of the incorporated PTC layer so as to decrease its internal resistance. The battery pack has a plurality of unit cells (1) placed side by side in parallel and the PTC device P to protect the unit cells (1) from overcurrents. The PTC device P has a first electrode (3) and a second electrode (4) connected to the both surfaces of the PTC layer (2). The PTC layer is formed to an outer shape that covers almost the entire of the end surfaces of the two unit cells (1) to which the first electrode (4) and the second electrode (4) are connected, and has through holes (2B) positioned against the end electrodes (1A) of the unit cells (1). The first electrode (3) and the second electrode (4) connected to the both surfaces of the PTC layer (2) are formed to an outer shape almost the same as the outer shape of the PTC layer (2); and the first electrode (3) and the second electrode (4) are connected to the end electrodes (1A) of the unit cells (1) at points where the through holes (2B) of the PTC layer (2) are located.