A laptop battery is just that. It is the battery pack that powers your laptop or notebook computer. Laptop batteries vary in size and shape depending on the style of laptop case they have to clip into. Most laptop batteries are rectangular and fit across the bottom, back section of a laptop.
Most laptop batteries are Lithium Ion powered; however, there are also a significant amount of NiMH (Nickel Metal Hydride) laptop battery packs as well. Lithium ion batteries are capable of packing more energy into the same volume of chemicals than NiMH, but they are considerably more expensive to produce. Lithium Ion laptop batteries are also less environmentally friendly than NiMH laptop batteries. Another downside to NiMH laptop batteries is that they lose their charge quicker when not in use than Lithium Ions laptop batteries, although this is not a concern for most people as they charge/discharge their laptop batteries every few days.