A rechargeable battery pack attachable to a power tool, the rechargeable battery pack comprising: a display element provided in such a manner that a lighted state thereof can be confirmed from outside; a remaining capacity detection device that is configured to detect a remaining capacity of a rechargeable battery ; a remaining capacity display control device that is configured to display the remaining capacity detected by the remaining capacity detection device by controlling the lighted state of the display element ; an abnormality detection device that is configured to detect an abnormality of the rechargeable battery ; and an abnormality display control device that is configured to display the abnormality of the rechargeable battery detected by the abnormality detection device by controlling the lighted state of the display element to an abnormality display state, which is different from a remaining capacity display state controlled by the remaining capacity display control device , wherein the abnormality detection device is configured to detect each of a plurality of kinds of abnormalities occurring in the rechargeable battery , wherein the abnormality display control device is configured to display the abnormality of the rechargeable battery in such a manner that a content of the abnormality can be identified by setting a lighting pattern of the display element in accordance with the content of the abnormality detected by the abnormality detection device , and wherein the abnormality display control device is configured to set the lighting pattern of the display element in such a manner that it can be identified whether or not the content of the abnormality detected by the abnormality detection device is a kind in which an abnormal state can be promptly restored to a normal state, when the battery pack is attached to a power tool, by an operation of the power tool by the user. a display element provided in such a manner that a lighted state thereof can be confirmed from outside; a remaining capacity detection device that is configured to detect a remaining capacity of a rechargeable battery ; a remaining capacity display control device that is configured to display the remaining capacity detected by the remaining capacity detection device by controlling the lighted state of the display element ; an abnormality detection device that is configured to detect an abnormality of the rechargeable battery ; and an abnormality display control device that is configured to display the abnormality of the rechargeable battery detected by the abnormality detection device by controlling the lighted state of the display element to an abnormality display state, which is different from a remaining capacity display state controlled by the remaining capacity display control device , wherein the abnormality detection device is configured to detect each of a plurality of kinds of abnormalities occurring in the rechargeable battery , wherein the abnormality display control device is configured to display the abnormality of the rechargeable battery in such a manner that a content of the abnormality can be identified by setting a lighting pattern of the display element in accordance with the content of the abnormality detected by the abnormality detection device , and wherein the abnormality display control device is configured to set the lighting pattern of the display element in such a manner that it can be identified whether or not the content of the abnormality detected by the abnormality detection device is a kind in which an abnormal state can be promptly restored to a normal state, when the battery pack is attached to a power tool, by an operation of the power tool by the user. <EOS>