Battery life is a measure of battery performance and longevity, which can be quantified in several ways: as run time on a full charge, as estimated by a manufacturer in milliampere hours, or as the number of charge cycles until the end of useful life. Build factors that affect battery life include the type, the number and the quality of cellsused. Generally, battery health and longevity declines further into a battery's life and as a function of the number of charge cycles it has gone through. However, there are a number of things a user can do to extend battery life. Both lithium polymer and lithium ion batteries tend to benefit from partial discharges to enable more charge cycles before performance is lost. Older rechargeables, like nickel cadmium or nickel metal-hydride lithium batteries, do not get a charge memory that reduces performance when the battery is only partially discharged before recharging. Because charge cycles degrade battery life, removing a laptops battery and plugging the device in when staying in one place will preserve and extend battery functioning. Other measures include ensuring clean electricity and keeping the device cool. Tips to increase the length of time a battery runs on a charge include not running more applications than necessary and reducing screen brightness