A battery pack comprising a lithium ion secondary battery and a current interrupting device for protecting the secondary battery, the secondary battery comprising positive and negative electrodes, a separator interposed between the positive and negative electrodes and a non-aqueous electrolyte, the current interrupting device comprising a recoverable device and a non-recoverable device, the recoverable and non-recoverable devices being connected in series with each other, and the non-recoverable device having an operating temperature of not less than 90.degree. C. and less than 150.degree. C.