A battery pack system may include a battery pack and a battery pack holder. The battery pack holder receives the battery pack and couples a battery pack terminal to a load associated with the battery pack holder. The battery pack includes an operation handle external to a battery pack housing. The operation handle is coupled to an operation member via an operation shaft that passes through the housing. A safety circuit of the battery pack couples power supplied by a battery to battery pack terminals based upon position of the operation handle. An operation member of the battery pack extends a locking member into an opening of the battery pack holder when the operation handle is in the engaged position, and retracts the locking member from the opening when the operation handle is in the disengaged position.