Mountain Lion suffers from a Mac that reduces battery life.
Apple now requires Mountain Lion users to have trouble with batteries recording the operation history and system information to investigate the cause. Some hypotheses are due to network connection errors, file system errors .
Arstechnica said that, through some real tests, they also felt Mountain Lion gave less battery life (tested on MacBook Air 2010). Previously, their MacBook Air 2010 gave about 4.5 hours of battery life when running with OS X Lion (when running a series of applications). Still running these applications, Mountain Lion only uses 3.5 hours, less than 20% less.