Ars Technica has been doing some testing after reports emerged that some Mountain Lion early adopters were experiencing degraded battery life after upgrading to OS X 10.8. A 46-page thread with nearly 700 replies has been growing over the past several weeks on the Apple Support Forums.
Ars writer Chris Foresman, after extended testing, discovered that the battery life of his Retina MacBook Pro review unit dropped 38% from its previous 8-hours. He was unable to narrow down blame for the battery loss to any particular bit of software or system process.
Our own testing revealed similar (and significant) drops in battery runtime after installing Mountain Lion. In previous tests, we were able to regularly achieve just over 8 hours of use by relying solely on our Retina MacBook Pro's integrated Intel HD4000 GPU. Performing the same "real-world" test using the same software applications and usage pattern, we never got the Retina MacBook Pro to run for more than a few minutes past 5 hours after a full charge.
Typically, the quad-core processor wasn't taxed beyond 5 percent capacity, except for occasional 10-20 percent spikes when loading webpages, reading or writing files, or other activities. Unexpected file system or network access, or less efficient use of the GPU, could cause additional power drain without showing significant CPU use.
One poster on Apple's support forums claims a company support representative told him that "an update will be issued via the [Mac App Store] as soon as they can work a fix."