Patent ID: 8410756

Claim:
A battery pack configured to supply electric power to an electric power tool, the battery pack comprising: a plurality of battery modules, each comprising at least one battery cell; a pack main body configured to: removably receive the plurality of battery modules, electrically connect the plurality of battery modules, and output electric power from the plurality of battery modules to the electric power tool; a movable member configured to: be movable to and from a first position with respect to the pack main body, and prohibit the plurality of battery modules from being attached to and removed from the pack main body when the movable member is at the first position; at least one sensor configured to detect whether the movable member is at the first position or not; at least one switch electrically connected in series with the at least one battery cell of the battery module; and a controller coupled with the at least one sensor and the at least one switch, and configured to turn off the at least one switch when detection by the at least one sensor indicates movement of the movable member from the first position.