Dell laptops use rechargeable lithium ion batteries for power when the laptop is not connected to the AC power adaptor. The batteries allow the laptop to run for a limited period of time before the laptop must either be connected to an electric outlet or have the batteries recharged. The batteries have a lifespan of around two years, or 400 discharge/charges. After that time, the battery may begin to lose its efficiency and hold a charge for less time, or not charge at all.
Turn the laptop off. Plug the AC power adaptor into the laptop. Allow the battery to completely charge for eight hours.
Unplug the power adaptor. Turn the laptop on. If the laptop does not turn on, the battery did not charge and should be replaced.
Allow the computer to remain on, using battery power. Time how long it takes for the battery to run out of life. Once the battery runs out of life, the computer will turn off. A Dell lithium ion battery should last for around three hours, based on many circumstances, such as the operating system and user activity. If the battery lasts for less than two hours, it's time to think about replacing the battery.