Abstract: The method of preventing battery over-discharge measures battery voltage with a control circuit, and switches an over-discharge protection switch connected in series with the batteries off with the control circuit when battery voltage drops below a minimum set voltage. Once the over-discharge protection switch turns to an off state, the off voltage at the output side of the switch is measured, and the over-discharge protection switch is held in the off state by this off voltage. When battery voltage rises above the minimum set voltage, return of the over-discharge protection switch to the on state is prevented.

Abstract: A secondary battery has a positive electrode principally comprising a lithium-containing complex oxide, a negative electrode principally comprising a carbon material and an organic electrolyte solution, said negative electrode utilizing a mixed binder comprising a polyamic acid and at least one polymer selected from the group consisting of a polyamide resin, polyvinylpyrrolidone and a hydroxyalkylcellulose. The battery has a long cycle life and, at the same time, hardly breaks or bursts even when the battery temperature becomes abnormally high, thereby being highly reliable.