Battery control device and motor drive system

A battery control device, comprising:

• an internal resistance detection unit that detects the internal resistance of a battery;
• a surface temperature detection unit that detects the surface temperature of the battery;
• an internal temperature estimation unit that estimates the internal temperature of the battery;
• a data storage unit that stores the surface temperature detected by the surface temperature detection unit and the internal resistance detected by the internal resistance detection unit in mutual correspondence, the surface temperature and the internal temperature being detected under a condition in which a difference between the surface temperature of the battery and the internal temperature of the battery is within a predetermined value;
• and
• an internal temperature diagnosis unit that diagnoses whether or not the internal temperature of the battery estimated by the internal temperature estimation unit is correct;
• wherein
• the internal temperature diagnosis unit, along with detecting with the internal resistance detection unit the internal resistance when the internal temperature was estimated by the internal temperature estimation unit, also searches for the internal resistance that corresponds to the surface temperature that is equal to the estimated internal temperature value from among the internal resistances stored in the data storage unit, and diagnoses the estimated internal temperature value on the basis of the result of comparison between the internal resistance that is a result of this search and the internal resistance detected during this internal temperature estimation.