Disclosed is a battery of a power tool, comprising a top cap, a bottom base, a battery body, and a movable assembly. The top cap and the bottom base are coupled to each other and define an accommodation space therein. The top cap forms a plurality of first recesses. The bottom base forms a plurality of through holes that communicate the outside, a first opening, and guide holes. The battery body is received in the accommodation space and comprises a plurality of guide tabs received in the guide holes. The movable assembly comprises a movable member and a plurality of springs. The movable member comprises projections, second recesses, and a plurality of second openings. The projections are received in the through holes. The springs are respectively set between the first and second recesses. When the projections are subjected to external forces and pushed thereby, it pushes the movable member to therefore compress the springs so as to have the second opening in communication with the first opening to show an open configuration for introducing external air for heat dissipation purposes. When the projections are no longer pushed by the external forces, the springs move the movable member back to make the second opening no longer communicating the first opening and thus closed.