A battery pack for detachably attaching to an electric tool provided with housing terminals, and the battery pack comprising: a battery pack cover; a battery pack base, joined to the battery pack cover to form a battery pack housing; a cell group, configured to charged and discharged, the cell group comprising several cells, and each cell being provided with a cell body portion, a first electrode terminal located on one side of the cell body portion, and a second electrode terminal located on the other side of the cell body portion; a battery terminal connector, electrically connected to the cell group, the battery terminal connector comprising battery pack terminals electrically connectable to the housing terminals and a terminal base supporting the battery pack terminals; a mounting cavity, defined in the battery pack housing, and accommodating the cell group and the battery terminal connector, the mounting cavity being formed with a socket for inserting the housing terminals to be electrically connected to the battery pack terminals; and a locking apparatus, capable of driving the battery pack and the electric tool to be locked connection or released, and the battery pack being characterised in that: a seal member blocking a passage from the socket to the cell group is disposed inside the mounting cavity; the battery pack further comprises a battery pack housing seal member blocking communication between the outside and the mounting cavity, and the battery pack housing seal member is disposed at a joint between the battery pack cover and the battery pack base; the locking apparatus is mounted on the battery pack housing, and the locking apparatus is isolated outside the mounting cavity; the locking apparatus is detachably mounted on the battery pack cover and is movable relative to the battery pack cover, to enable the battery pack and the electric tool to be locked connection or released; and a retaining cavity that is concave is provided in an outer surface of the battery pack cover and at least partially surrounds the locking apparatus, the retaining cavity forms a movement space for the locking apparatus to move, and the retaining cavity and the mounting cavity are not in communication with each other. a battery pack cover; a battery pack base, joined to the battery pack cover to form a battery pack housing; a cell group, configured to charged and discharged, the cell group comprising several cells, and each cell being provided with a cell body portion, a first electrode terminal located on one side of the cell body portion, and a second electrode terminal located on the other side of the cell body portion; a battery terminal connector, electrically connected to the cell group, the battery terminal connector comprising battery pack terminals electrically connectable to the housing terminals and a terminal base supporting the battery pack terminals; a mounting cavity, defined in the battery pack housing, and accommodating the cell group and the battery terminal connector, the mounting cavity being formed with a socket for inserting the housing terminals to be electrically connected to the battery pack terminals; and a locking apparatus, capable of driving the battery pack and the electric tool to be locked connection or released, and the battery pack being characterised in that: a seal member blocking a passage from the socket to the cell group is disposed inside the mounting cavity; the battery pack further comprises a battery pack housing seal member blocking communication between the outside and the mounting cavity, and the battery pack housing seal member is disposed at a joint between the battery pack cover and the battery pack base; the locking apparatus is mounted on the battery pack housing, and the locking apparatus is isolated outside the mounting cavity; the locking apparatus is detachably mounted on the battery pack cover and is movable relative to the battery pack cover, to enable the battery pack and the electric tool to be locked connection or released; and a retaining cavity that is concave is provided in an outer surface of the battery pack cover and at least partially surrounds the locking apparatus, the retaining cavity forms a movement space for the locking apparatus to move, and the retaining cavity and the mounting cavity are not in communication with each other. a seal member blocking a passage from the socket to the cell group is disposed inside the mounting cavity; the battery pack further comprises a battery pack housing seal member blocking communication between the outside and the mounting cavity, and the battery pack housing seal member is disposed at a joint between the battery pack cover and the battery pack base; the locking apparatus is mounted on the battery pack housing, and the locking apparatus is isolated outside the mounting cavity; the locking apparatus is detachably mounted on the battery pack cover and is movable relative to the battery pack cover, to enable the battery pack and the electric tool to be locked connection or released; and a retaining cavity that is concave is provided in an outer surface of the battery pack cover and at least partially surrounds the locking apparatus, the retaining cavity forms a movement space for the locking apparatus to move, and the retaining cavity and the mounting cavity are not in communication with each other.