Battery pack

The battery pack has a plurality of batteries 1, and battery holders 2 that dispose the batteries 1 in multiple rows and columns and in parallel orientation. The battery holders 2 are provided with insertion sections 21 separated by dividing walls 22 where batteries 1 are inserted and held in fixed positions. Each battery 1 contacts the dividing walls 22 in a thermally coupled manner to transfer and dissipate heat generated by the batteries 1 to the battery holders 2. Further, the thickness of the battery holder 2 dividing walls 22 increases from the periphery (surface) regions to the center regions making the heat capacity of the dividing walls 22 thermally coupled with batteries 1 disposed in center regions of the battery holders 2 greater than the heat capacity of the dividing walls 22 thermally coupled with batteries 1 disposed in periphery regions of the battery holders 2.