1. Field of the Invention
The present invention relates to a battery unit and an information processing apparatus having the battery unit mounted therein. More particularly, this invention is concerned with a battery unit capable of monitoring the state (amount of remaining power or deterioration) of a cell with high precision and an information processing apparatus having the battery unit mounted therein.
2. Description of the Prior Art
Due to the trend toward downsizing information processing apparatuses, there is an increasing demand for portable apparatuses including notebook-type personal computers. In a portable apparatus, a battery is incorporated as a power source. When the portable apparatus is used in an environment in which an ac voltage cannot be obtained from the mains, it can be driven by a battery. More and more portable apparatuses are therefore including a secondary battery that can be used cyclically as a battery. A form of the secondary battery is a battery unit that is a battery pack having a plurality of cells connected in parallel with one another. This form is intended to cope with a large power consumption of an apparatus.
For detecting an amount of remaining power in such a battery unit, normally, the battery unit is connected to a main unit of an information processing apparatus. The battery unit supplies power to a load in the main unit. In other words, a no-load voltage provided by the battery unit is estimated based on a discharge current flowing into the load or a voltage produced by a cell. According to this technique for detecting an amount of remaining power, there is a problem that it is hard to detect an amount of remaining power accurately because a voltage varies depending on a change in current flowing through a load.
Moreover, since a plurality of cells is packed in the form of a battery unit, it is impossible to detect the state of the battery unit in units of a cell. If an amount of remaining power is unequal among the cells, part of a current to be supplied to a load may flow into a cell having a small amount of remaining power. This invites deterioration of a driving ability. Moreover, when the battery unit is charged, a phenomenon that a cell having a large amount of remaining power discharges towards a cell having a small amount of remaining power may take place. This poses a problem that an excess current may flow into the cell having a small amount of remaining power to eventually break down the cell.