The battery refers to the device that could turn chemical energy, solar energy, atomic energy or other forms of energy into electrical energy. It is divided into once battery (commonly known as dry battery), and twice batteries ( repeatly rechargeable battery ), With the advancing and  development of technology, battery has experienced a long process from the initial photovoltaic cell to the nickel-cadmium batteries, nickel-metal hydride batteries, lithium batteries (including the lithium metal batteries and lithium polymer batteries),to current developing fuel cells. Each technological innovation does not only make major breakthrough  of batteries in terms of volume, weight and ease of use , but also make the battery become more environmentally friendly.

If CPU is the brain of notebook, the laptop battery is  undoubtfully  the heart –a source of energy. The main features of laptop “portable computing” also depens on a tiny piece of the battery to provide. Laptop battery has undergone tremendous changes, regardless of their size, capacity and type. Each leap of laptop has a great relationship with its battery , but  manufacturers seem to have overlooked this aspect of publicity, resulting in users paying little attention to the very important part of laptop and little understanding of laptop battery . Laptop is mainly used of rechargeable nickel-cadmium, nickel hydrogen, or  lithium batteries,which are the main source now.