Big notebook vendors base their battery numbers on Jeita, a method that involved first measuring the machine at complete idle, with the screen and other settings turned to minimum, and seeing how long the laptop lasted. Then, with different settings, measuring the machine again while playing a movie file on the screen, finally averaging the two results.
But more often than not, the results didn’t add up: PC Authority reports that Sony stated up to 11 hours for the Vaio VGNTZ36GNW in their review, but really only lasted for four to eight hours. Sony says it will now be advertising the second result only. To compare,here’s an example of the old method Sony used to measure battery life, while here’s the new method, called “Jeita A.”
