<P> Pure lithium is highly reactive . It reacts vigorously with water to form lithium hydroxide and hydrogen gas . Thus, a non-aqueous electrolyte is typically used, and a sealed container rigidly excludes moisture from the battery pack . </P> <P> Lithium - ion batteries are more expensive than NiCd batteries but operate over a wider temperature range with higher energy densities . They require a protective circuit to limit peak voltage . </P> <P> For notebooks or laptops, lithium - ion cells are supplied as part of a battery pack with temperature sensors, voltage converter / regulator circuit, voltage tap, battery charge state monitor and the main connector . These components monitor the state of charge and current in and out of each cell, capacities of each individual cell (drastic change can lead to reverse polarities which is dangerous), and temperature of each cell and minimize the risk of short circuits . </P> <P> Li - ion cells (as distinct from entire batteries) are available in various shapes, which can generally be divided into four groups: </P>

What type of battery is used in laptops