Notebook computers obtain operational power from either rechargeable battery packs for full stand-alone use, or AC power for use conveniently close to power outlets. Docking stations also are designed to plug into AC power, and to provide that power to the notebook computer. Most of the time, a notebook computer is driven by a battery power source. As a portable power source for portable electronic devices such as notebook computers, digital cameras, or video cameras, a rechargeable battery pack is used. While a portable computer is in use on AC power, it takes advantage of the available AC power and recharges the battery pack. The battery pack can also be removed from the portable computer and charged separately. The battery is housed in the palm rest in front of the keyboard of a keyboard housing, or behind the keyboard. Power management functions are prepared for extending the battery driving time. One of the power management functions is the suspend mode in which power supply is stopped, except for the some devices including a memory in which the data necessary for returning to the present status of the system is stored. When a suspend mode signal is occurred, the system is controlled so that the status of the CPU (central processing unit) and the status of various peripheral devices just before the suspend mode is saved to the memory and the power is provided to only some devices such as the memory etc. The battery connector is assembled with the base for electrically connecting the battery to a power supply circuit of the notebook computer. In a laptop computer, a battery pack has flat and rectangular shaped top and bottom.

Battery chargers in notebook computers are generally used to control battery charging and/or power distribution to a system. Laptop computers can be used under battery power that is directly related to ability to apply a recharge to the battery and the ability of the battery to retain a charge. When battery is charged, a constant-current is continuously supplied to the battery in an early charging stage, which is called a constant-current charging mode. When the constant current is continuously supplied, an output voltage of the battery increases. When the output voltage of the battery reaches a predetermined voltage, an internal or external charging control part controls a voltage supplied to the battery not to increase higher than the predetermined voltage so as to prevent the battery from being overcharged. Hence, the battery is continuously charged at a constant voltage, which is called a constant-voltage charging mode. The battery pack usually includes a rechargeable battery and a protective circuit for protecting the rechargeable battery from overcharging, overdischarging, or other troubles. Without the protective circuit, batteries such as lithium ion batteries for use in notebook PCs are likely to burst if they are overcharged during charging. On the other hand, if they are discharged exceedingly above its allowable limit, their charging/discharging characteristics are deteriorated.

A battery converts chemical energy within its material constituents into electrical energy in the process of discharging. Generally, batteries are divided into two groups: primary batteries, which are non-recoverable once used and rechargeable batteries, which are recoverable. Primary batteries that meet this demand are lithium primary cells having an anode of lithium metal which are small is size and light in weight and yet have a high capacity. Rechargeable batteries are chemical cells capable of charging and discharging. The rechargeable battery is generally returned to its original charged state by passing an electrical current in the opposite direction to that of the discharge. There are various kinds of secondary batteries, including nickel-cadmium (Ni--Cd) batteries, nickel-metal hydride (Ni-MH) batteries, lithium ion batteries, lithium polymer batteries, lithium-metal secondary batteries, and zinc-air storage batteries. Rechargeable batteries such as lead batteries, nickel-cadmium batteries, and nickel-hydrogen batteries can be used repeatedly, but they are low in operating voltage because they rely on an aqueous electrolytic solution. Therefore, they are not suitable for use which requires high capacity, small size, and light weight. Lithium ion batteries have become popular because they have a high energy density and high operating voltage, excellent conservation and life properties and are environmentally friendly.

Lithium batteries have been introduced into the market because of their high energy densities and high unit cell voltage. A lithium ion battery is characterized by its anode and cathode active materials made of a substance capable of occluding and releasing lithium ions. Lithium batteries work without requiring electrodeposition of lithium metal. Lithium is atomic number three on the periodic table of elements, having the lightest atomic weight and highest energy density of any room temperature solid element. Lithium secondary batteries are classified as lithium ion batteries, lithium ion polymer batteries, and lithium polymer batteries according to kinds of separator and electrolyte. Lithium batteries can be either lithium ion batteries or lithium metal batteries. Lithium ion batteries intercalate lithium ions in a host material, such as graphite, to form the anode. On the other hand, lithium metal batteries use metallic lithium or lithium metal alloys for the anode. Lithium batteries are widely being used as power supplies for portable electronic devices such as notebook computers, camcorders or mobile phones.