Battery pack and cordless electric tool that has this

A compact battery pack with a high handling ability, and a restraining the deterioration of the battery cells. The battery pack includes an insertion portion to be inserted into a handle portion of a cordless power tool, and a receiving portion receivable in the all battery cells. A protective circuit board with a protection circuit that protects batteries from overcharging and over-discharging, is installed in the insertion section. A switching element is connected between the battery cells and a driving motor of the power tool. An air passage in communication with the battery pack and a main housing of the cordless power tool is formed within the handle. The switching element is positioned in the air passage.