A battery pack includes at least one battery cell having first and second end portions spaced apart from each other in a length direction of the at least one battery cell, and an outer peripheral surface between the first and second end portions, a circuit board connected to the at least one battery cell, the circuit board to monitor the at least one battery cell, and a sensor extending from the circuit board toward the at least one battery cell, the sensor contacting the outer peripheral surface of the at least one battery cell, and the sensor having a casing having a first surface that is concave toward the outer peripheral surface of the at least one battery cell, a thermistor chip inside the casing, a lead wire extending from the thermistor chip outside the casing, and a filler inside the casing.