Secondary battery device and method of protecting an overdischarge of the same

A secondary battery device comprising:

• a secondary battery comprising a series combination of a plurality of unit batteries for supplying electric power into a load circuit;
• a load state judging unit for judging an operation state of said load circuit;
• a total voltage detecting unit for detecting a total terminal voltage of said plurality of unit batteries;
• and
• an overdischarge protective unit connected to said plurality of unit batteries for detecting a discharged state of each of said unit batteries and breaking the discharge from said secondary battery when any of said unit batteries reaches a predetermined overdischarge state, said overdischarge protective unit allowing the supply of electric power into said load circuit to continue without breaking the discharge from said secondary battery if the total terminal voltage is not lower than a predetermined total reference voltage, when said load state judging unit judges that said load circuit stays in a predetermined operation state requiring a protection of power supply.

A method of protecting an overdischarge of a secondary battery, said method comprising:

• supplying electric power into a load circuit;
• judging an operation state of said load circuit;
• and
• detecting a discharged state of said secondary battery and breaking the discharge from said secondary battery when said secondary battery reaches a predetermined overdischarged state,
• wherein the supply of electric power into said load circuit continues without breaking the discharge from said secondary battery when said load circuit is judged that it stays in a predetermined operation state requiring a protection of power supply.