DEVICE FOR ESTIMATING INTERNAL TEMPERATURE OF BATTERY FOR POWER TOOL, AND DEVICE FOR POWER TOOL

An internal temperature estimation unit, which reads a detected temperature of a cell of a battery for an electric power tool to estimate an internal temperature of the battery based on the detected temperature, includes: an initial-value setting device which reads, when a discharge/charge of the battery is started, the detected temperature and sets the detected temperature as an initial value; and a temperature increase amount calculation device which calculates a temperature increase amount of the cell of the battery based on a latest value of the detected temperature and the initial value set by the initial-value setting device; the internal temperature estimation unit outputs the temperature increase amount as an estimated value representing the internal temperature of the battery.