Abstract: A battery unit includes a plurality of cells connected in parallel with one another, and a switch connected in series with at least one of the cells. The battery unit further includes a control circuit for controlling the on or off state of the switch, and a voltage detection terminal at which a voltage produced by a cell, to which the switch is connected, is developed. The switch can be turned off even with the battery unit connected to a load. A cell in series with which the switch is connected is disconnected from the load. In this state, the state of the cell can be detected through the voltage detection terminal. Even when a resistor is substituted for the switch, the same advantage can be provided. Moreover, the battery unit is freely detachably attached to a main unit of an information processing apparatus. The battery unit then supplies power to the main unit. A power supply control circuit for requesting notification of the state of each cell in the battery unit is incorporated in the main unit.

Abstract: A protection circuit is used for a battery unit which has a plurality of cell parts coupled in parallel, and first and second power supplying terminals, where each of the cell parts includes a plurality of battery cells coupled in series, and first and second terminals respectively coupled to the first and second power supplying terminals. The protection circuit includes a plurality of switching elements making an electrical connection to the first terminal of a corresponding one of the cell parts and the first power supplying terminal, and disconnecting the electrical connection in response to an active signal, and a voltage monitoring circuit outputting the active signal to the switching elements when a voltage of at least one battery cell within one cell part falls outside a predetermined range, independently with respect to each of the cell parts.