Update: The final builds of 10.8.2 and 10.7.5 were released by Apple on September 19. We have put those builds through the same test and the results can be found here.

Last month we performed a series of battery life tests on three Mac laptops: a 2011 15-inch MacBook Pro, 2012 15-inch MacBook Pro with Retina Display, and a 2011 13-inch MacBook Air. We were able to demonstrate that the upgrade to OS X 10.8 Mountain Lion caused a significant reduction in battery life and that Mountain Lion’s first update, 10.8.1, only partially restored the lost running time.

In response to our reports, we received many questions and suggestions for further testing, with some readers telling us that they experienced a similar loss in battery life after the upgrade from 10.6 Snow Leopard to 10.7 Lion. Other readers wanted to know if there would be a significant difference in battery life if the tests were run on a solid state system drive (SSD) versus a traditional hard disk system drive (HDD).

In an effort to provide a comprehensive look at battery life, we decided to take one of our test Macs back to Snow Leopard and test each build of OS X from 10.6.8 all the way to the current build of Mountain Lion on both an SSD and an HDD. We hope that our tests will answer some questions about a Mac’s battery life “journey” though the many iterations of OS X over the past few years.

Testbed

Our test computer is a 2011 15-inch MacBook Pro at 2.0 GHz with 8 GB of RAM, a Radeon HD 6490M GPU, and two internal drives: an OCZ Vertex 4 64 GB SSD and a Seagate Momentus 750 GB HDD (we used an Other World Computing Data Doubler bracket to replace the MacBook Pro’s optical drive with the Seagate hard drive).

Our test MacBook Pro, which readers should note is a different computer than the one used in our first tests, has been lightly used during its life. Its battery at the start of the tests had 159 cycles and was considered healthy by OS X. The excellent coconutBattery utility showed that the battery’s capacity was still at 95 percent of its theoretical maximum.

Using the MacBook’s original system installation discs (remember the good old days when Apple used to include those?), we erased the internal drives and installed the version of OS X that the system shipped with, 10.6.6, to both drives so that we could individually test battery life on the SSD and HDD. We then updated each installation to 10.6.8, the last version of Snow Leopard released by Apple.

Testing Methodology

For each test, starting with OS X 10.6.8, we allow the battery on the Mac to reach a full charge. We then disable all applications and services except for WiFi, set the screen to 50 percent brightness, turn keyboard illumination off, disable the screen saver, and set the power and display to remain on indefinitely.

To simulate a moderate workflow, we use a custom Automator application, which is the same as in our previous tests. Our automatic workflow consists of the following steps:

Open TextEdit, pause 10 seconds Open Safari and navigate to a content-heavy website (macobserver.com), pause 20 seconds Navigate to a second content-heavy website (cnn.com), pause 20 seconds Open Mail, pause 10 seconds to allow any messages to download Close all open applications Log a time stamp to a text file Repeat

Regarding the Safari Web browser, which is launched as part of the tests, we used the version of Safari that was common to each edition of OS X at its launch. This means that our Snow Leopard tests use Safari 5.0.5, Lion tests use Safari 5.1.7, and Mountain Lion tests use Safari 6.

The one exception is Safari 6 on 10.7.4, with which we performed an additional test (noted with an asterisk on the chart) to determine if different versions of Safari had any impact on battery life.

To determine the battery life achieved with each test, we use the time stamp created by our Automator workflow to calculate total running time.

Each version of OS X is tested at least twice on each storage medium. We then compare the results and, if the difference between the results is less than 5 percent, we average them. If the difference is greater than 5 percent, we run multiple tests until we can determine which result was abnormal and why. We then discard the abnormal result and average the remaining results.

At the suggestion of some readers, we performed a PRAM and SMC reset following the completion of each test and the installation of the next OS X update. Although we designed our Automator workflow so that it would not trigger the MacBook’s discrete GPU, we also installed Cody Krieger’s gfxCardStatus utility and set it to force the use of the integrated GPU only throughout our tests, just to be safe.

Test Results

As the chart illustrates, there was a definite and noticeable reduction in battery life with the upgrade from Snow Leopard to Lion. In both the SSD and HDD configurations, we measured a roughly 40 minute reduction in running time. This loss in battery life persisted until 10.7.3, which restored running time to 10.6.8 levels.

10.7.4 maintained the battery life that was regained by the 10.7.3 update, and there appears to be no significant difference between using Safari 5.1.7 and Safari 6 in terms of running time.

Just as we saw in our previous tests, the upgrade to 10.8 Mountain Lion decreased battery life significantly, by about 1 hour and 45 minutes, or 30 percent. The upgrade to 10.8.1 restored about 30 minutes of battery life for our MacBook Pro, an improvement for sure, but not nearly enough to regain lost ground.

The big change came with 10.8.2, which is still undergoing developer testing. Using what was the latest build when the tests were run, 12C35 (a newer build, 12C43 was released September 5), we saw a tremendous increase in battery life, to the point where running time was a few minutes longer than even that of 10.6.8.

We must reiterate that 10.8.2 is still a work-in-progress and is subject to change before it is released to the public. We do not know what changes Apple has made to Mountain Lion’s code to account for the battery life increase, or if those changes must necessarily be reversed before release, but we hope that Apple will find a way to preserve the battery life improvements in future Mountain Lion updates.

Hard Disk Drive vs. Solid State Drive

Although battery life across the various iterations of OS X follows the same trend between the SSD and HDD, the HDD achieves between 10 and 20 minutes of additional battery life over the SSD.

In addition to their significantly improved performance, SSDs are also marketed as energy-sipping power savers when compared to traditional hard drives. In our case, however, the design of the test and specific drives used made the HDD the winner in battery life.

According to Western Digital, the Scorpio Blue HDD uses 1.4 Watts of power during active reads and writes and 0.59 Watts at idle, while the high performance OCZ Vertex SSD uses 2.5 Watts while active and 1.3 Watts at idle.

This slight difference in power draw, combined with a workload that is primarily idle, accounts for the 10 to 20 minute battery life advantage we saw with the HDD. So if you need the absolute best battery life for light workloads, a low speed, energy efficient traditional hard drive may be the way to go. Considering the large performance and reliability advantage that a solid state drive has over a traditional hard drive, however, the majority of consumers would be better suited with the SSD, even at the expense of a few minutes of running time.

Conclusions

It is clear that Apple has released the last two versions of OS X with serious underlying code issues that noticeably reduce battery life. The good news, however, is that the Cupertino engineers have worked to remedy the issues within the first two or three point updates to each OS.

Customers still on Snow Leopard who have hesitated upgrading to Lion due to battery life issues should feel comfortable upgrading, as 10.7.4 performs nearly as well as 10.6.8 in terms of running time.

However, customers who depend on their battery life — with all other considerations being equal — should wait to upgrade to Mountain Lion until the public release of 10.8.2. As we mentioned above, although the developer builds of 10.8.2 are very promising, nothing can be guaranteed until the final version of the software has been approved.

We will continue to monitor the development of OS X Mountain Lion and test new updates to the OS as they are released. Until then, we look forward to the final build of 10.8.2 and the promise of complete battery life restoration.

Teaser graphic via Shutterstock.