BATTERY PACK

A battery pack comprises a housing having a bottom portion (211) with water drain holes (25). An opening end edge of the drain hole (25), which is disposed at the outer portion of the housing case (20), is set as an outer end edge (261); an opening end edge of the drain hole (25), which is disposed at the inner portion of the housing case (20), is set as an inner end edge (262). The shape of the outer end edge (261) of the drain hole (251) is set so that the outer end edge (261) slightly rises toward the inside of the housing case (20) as compared with a support lower surface (201) of the housing case (20) that corresponds to the peripheral portion of the outer end edge (261). For this reason, a clearance C is formed between the outer end edge 261 and the placement surface F with which the support lower surface 201 of the housing case 20 corresponding to the peripheral portion of the outer end edge 261 comes into contact. Accordingly, even when the battery pack (10) mounted on the tool body (not shown) is placed on a desk or the ground such that the support lower surface (201), which is the bottom portion of the battery pack (10), comes into contact with the placement surface F, the outer end edge (261) of the drain hole (25) is positioned above the placement surface F by the clearance C.Therefore, it is possible to prevent the drain hole (25) from being closed by the placement surface F, and hence it is possible to discharge the water.