Abstract: A battery charge circuit using a constant voltage/constant current to power charge a plurality of battery packs, a current detection circuit to detect a charge current according to a predetermined value, and control mechanisms to maintain a constant voltage charge mode when the charge current value drops below a set value within the battery pack.

Abstract: In a battery-driven portable computer, a battery pack is constituted by m battery sets connected in series each including n lithium-ion secondary battery cells connected in parallel. A voltage monitor for monitoring the voltage of the terminal electrode of each battery set and a charger for independently appropriately charging each battery set in accordance with a monitor result are arranged, thereby realizing battery driving by a lithium-ion secondary battery pack having a large capacity. A computer system monitors the voltages of the battery cells which are part of a secondary battery by comparing the battery voltages with a predetermined voltage value in order to detect overdischarge (undervoltage) or overcharge (overvoltage), outputs this information outside of the battery pack, and terminates processing prior to a circuit disconnect.