The unscientific test from The Mac Observer pitted numerous revisions of OS X, from 10.6 Snow Leopard to 10.8.2 Mountain Lion developer build 12C35, against each other to determine how the operating system effects battery life.
The test used a 2011 15-inch MacBook Pro running a 2.0 GHz i7 processor with 8 GB of RAM, a Radeon HD 6490M GPU and two internal hard drives, an OCZ Vertex 4 64 GB SSD and a Seagate Momentus 750 GB HDD.
Each operating system was tested at full charge, with all applications and services disabled save for Wi-Fi, screen adjusted to 50 percent brightness with display set for continuous use and screen saver disabled. A moderate workflow was simulated using a custom Automator application, which repeated until the battery was fully drained.
Source: The Mac Observer
Using OS X 10.6.8 Snow Leopard as a baseline, the compiled test data showed a significant hit to battery performance with the introductions of 10.7 Lion and 10.8 Mountain Lion. Upon release, Lion lost over 40 minutes of battery life and took three revisions to regain Snow Leopard power efficiency. In contrast, Mountain Lion saw a huge 105 minute loss in battery performance when it was released in July, with the latest 10.8.1 version moving the OS only 30 minutes closer to baseline.
With OS X 10.8.2, however, battery life is not just brought back in line with Snow Leopard levels, but the OS actually outperforms its predecessor by eight minutes. This marks an 88.5 minute savings in power consumption from the most recent 10.8.1 version of Mountain Lion.
It was previously reported that Apple's Mountain Lion was causing battery life issues for many users, with some MacBook Air owners seeing their batteries lasting half as long as when OS X 10.7 Lion was installed. Subsequent tests of the latest public version of OS X, Mountain Lion 10.8.1, showed Apple engineers were working on a fix as battery life was substantially improved. If Monday's tests are accurate, OS X 10.8.2 will bring further battery life improvements, perhaps besting even the legacy OS X 10.6 Snow Leopard.
While the final public version of OS X 10.8.2 may not boast power savings identical to the home-brew test, the developer builds are promising and show Apple is taking an aggressive stance in solving the battery degradation issues seen at Mountain Lion's launch.