In a battery pack which comprises: a battery set composed of two or more lithium battery cells connected in series; a first protection circuit including a first voltage detect part for detecting the voltage(s) of a part of the two or more battery cells, and a first signal output part for issuing an output signal when a detect voltage detected by the first voltage detect part goes below a given over-discharge judgment voltage value; a second protection circuit including a second voltage detect part for detecting the voltage(s) of another part of the two or more battery cells, and a second signal output part for issuing an output signal when the detect voltage of the battery cell detected by the second voltage detect part goes below a given over-discharge judgment voltage value; and, a switch which is connected to the current path of the battery set and can be turned on or off according to the output signals of the first and second signal output parts and, there is further provided dead time means connected between the second signal output part of the second protection circuit for issuing an output not responding to a variation in an input signal occurring within a given time.