updated 07:53 pm EDT, Mon September 10, 2012
Lion still 'king' of battery life among released versions
First, the bad news: three sets of separately-conducted independent tests have confirmed what many users suspected -- the initial release of Mountain Lion contained a bug that severely decreased battery life in the latest MacBook models compared to previous releases. The good news is that those same tests show that the not-yet-released 10.8.2 update, currently in beta testing, may fix the issues -- and possibly provide slightly better battery life than has been previously seen in any OS version tested, going back to Snow Leopard.
Tests done by Ars Technica last month and more recently The Mac Observer and our own MacNN Labs all agree that while the 10.8.1 update mitigated the problem somewhat, an unknown flaw in OS X 10.8.0 could -- on 2011 and newer MacBooks particularly -- resulted in up to 38 percent loss levels, meaning in some cases over 100 minutes less battery life compared to the latest version of Lion (10.7.4), which all three testing groups found had the best battery levels of the released versions tested. Older models do not seem to have been affected, or the drop in battery time was less noticeable with older battery technology.
Apple is clearly aware of the problem, as the release of 10.8.1 improved battery life some 20 percent compared to 10.8.0, but levels were still down significantly from those achieved by 10.6.8 (the final release of Snow Leopard) and 10.7.3 and higher of Lion. It should be noted that the initial release of Lion (10.7.0) also saw a significant drop in battery life, which was restored to 10.6.8 levels over the course of the first three bug-fix updates, so there is a precedent for 10.8.0's behavior -- though the drop in the first version of Lion was noticeably less severe, about a half-hour's drop in battery life.
Ars Technica was the first to test and report on the problem, noting that a just-released Retina MacBook Pro went from eight hours of use time to just over five hours under 10.8.0. TMO has since followed up with a test done on a 2011 MacBook Pro, which included the second build of 10.8.2 (12C35) released to developers and a wide range or system versions from 10.6.8 on up. For their tests, the second build of 10.8.2 showed a full restoration to previous highs (and just a little more, actually) in terms of battery life, fully resolving the issues brought about by 10.8.0.
Our own independent testing lab has been trying out the later build of 10.8.2 with a third-generation 11-inch MacBook Air, a 2010 15" MacBook Pro, a 2012 13-inch MacBook Pro and a 15-inch 2012 Retina MacBook Pro. Our results so far are not as clear-cut a victory for 10.8.2 as TMO's tests found, but results vary by machine and further testing is currently underway. MacNN currently still recommends 10.7.4 as the best recent OS version for maximum battery life on current and recent MacBook computers, though 10.8.2 appears to be well on its way to resolving the issue.