A battery pack, comprising a first cell and a second cell connected in series, the first cell having a current cut-off device and having a first failure voltage, the current cut-off device being configured to be able to break a circuit in response to a voltage value of the first cell reaching or exceeding the first failure voltage, and the second cell having no current cut-off device. The battery pack may use a soft pack battery as the second cell, having advantages such as high energy density, low impedance, high discharge power, a low rate of temperature rise during high-rate discharge, and flexibility in dimensions.