Ensure the laptop is turned off. Plug the AC power adapter into an electric outlet. Insert the circular end into the appropriate hole on the side of the laptop.
Leave the laptop off. Allow the AC power adapter to fully charge the battery for 12 hours. During this time, do not use the laptop or turn it on. This can slow down the charging of the battery.
Remove the AC power adapter by gently pulling it out of the hole on the side of the computer. Turn the laptop on by pressing the "Power" button. Note what time you turned the laptop on.
Allow the laptop to use the battery power until the battery dies and the laptop turns off. Note what time the laptop dies. During this time, you can use your laptop if desired.
Compare the start time to the end time. If the battery does not last for at least an hour, the battery efficiency is decreasing and/or the battery may be dying and should be replaced. The battery should be tested routinely to compare efficiency levels. Once the efficiency significantly decreases, the battery should be replaced.