Provided is a low-cost battery pack capable of predicting a remaining battery life of a rechargeable battery with more accuracy while being capable of dealing with a variation in battery characteristics. In a remaining battery life prediction device, a constant current source configured to cause a constant current to flow through a battery as a load current is provided, battery voltages before and after the constant current as the load current is caused to flow through the battery are measured at a plurality of time points, and a battery internal resistance is calculated based on a change over time of the battery voltage.