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.