At the launch MacBook Air 2013 Apple Lossless Audio CODEC (ALAC), announced that its laptops are capable of obtaining up to 12 hours of battery autonomy for normal use, OS X Mountain Lion being used for tests. What Apple said then is no longer valid, because now its Airs get up to 15 hours of satisfied autonomy OS X Mavericks and we are talking about an increase of over 3 hours in terms of the period of use. For tests it was used a script that combines web browsing on certain websites and text editing, and the results provided an average of 15 hours of use for the new Macs.
I suspect the aggressiveness of the auto-playing Flash ads that happen to be on specific websites on a particular day may partly explain the huge variability in Mountain Lion's numbers. Some of the lower-scoring Mountain Lion trials may have also had the bad luck to coincide with energy-intensive periodic jobs—jobs that are prevented from running on Mavericks due to AC power or battery-level restrictions as part of centralized task scheduling. These tests may or may not be representative of how you use your Mac, but regardless, it's clear that Apple's efforts have not been in vain. Mavericks really does consume less energy than Mountain Lion when performing the same tasks.
Although they are not as radical, there are also improvements in the case of old Macs, a MacBook Pro 2007 obtaining a few tens of minutes of extra autonomy after installation OS X Mavericks. Practically, the new technologies implemented in OS X Mavericks improve so much the system for managing applications that run in the background and manage energy so efficiently, that in the end we can get up to 3 more hours of use in the case of MacBook Airs and probably between 1 and 2 additional hours on MacBook Pros.
