A battery deterioration judging system includes a memory, and a processor coupled to the memory. The processor is configured to acquire a state amount of a battery, derive a first deterioration probability of the battery, based on the state amount of the battery and a predetermined first calculation model, derive a reliability degree of a second calculation model, which is different than the first calculation model, based on a number of state amounts, derive a second deterioration probability of the battery, based on the state amount of the battery and the second calculation model, and judge deterioration of the battery based on the reliability degree, and at least one of the first deterioration probability or the second deterioration probability.