The Unexpected: Battery Life in OS X vs. Windows Vista

A while ago I started testing the Lenovo X300 with hopes of comparing it to Apple's MacBook Air. The review never saw the light of day but the testing was mostly complete. Obviously the X300 doesn't run OS X, but the MacBook Air can run Windows so I compared battery life between the two under Vista, which yielded some unexpected results.

There are no scripted battery life tests under OS X, while under Vista we have things like MobileMark - luckily, the tests I've put together for OS X can easily be reproduced under Vista. Let's take a look at my tests under OS X:

The wireless web browsing test uses the 802.11n connection to browse a series of 20 web pages varying in size, spending 20 seconds on each page (I timed how long it takes me to read a page on Digg and came up with 36 seconds; I standardized on 20 seconds for the test to make things a little more stressful). The test continues to loop all while playing MP3s in iTunes.

The DVD playback test is simple: I play Blood Diamond in a loop from an image on the hard drive until the battery runs out.

The final test is the multitasking workload. For this benchmark I'm downloading 10GB worth of files from the net (constant writes to the drive), browsing the web (same test as the first one) and watching the first two episodes of Firefly encoded in a 480p XviD format (Quicktime is set to loop the content until the system dies).

The system was set to never shut off the display and never go to sleep, although the hard drive was allowed to spin down when possible. The display brightness was set at 9 blocks (just over 50%), which I felt was comfortable for both day and night viewing.

The first test was easy to duplicate under Vista; web browsing is ubiquitous across platforms and iTunes has been cross platform for a while now. The same goes for the DVD playback test; instead of using Apple's DVD app I just used Windows Media Player 11 under Vista. And the final test also translates flawlessly to Vista.

Below are the results I got when I first ran the MacBook Air under both OS X and Vista:

Note that this is the same hardware and with the same brightness settings under both OSes. Vista's power management was set to Balanced and the display was set to never turn off under both OSes; the hard drives were free to spin down if possible.

The results are pretty staggering. The same usage model under both OSes results in a significant advantage for OS X. I basically got twice the battery life under OS X as I did under Vista. Now it is possible that Apple's power management is simply more sophisticated under OS X and not optimized for Vista, but what inspired me to include this in today's review was actually something AnandTech's own Jarred Walton brought up in a meeting earlier this week.

In testing the first batch of Centrino 2 notebooks that Jarred received he noted that he can't seem to find a mainstream notebook with a 50 - 60WHr battery that can come close to offering the sort of battery life you get out of the Macs. Even in his idle tests (just leave the computer at the desktop without doing anything or putting it to sleep) Jarred has been finding many mainstream notebooks only seem to last 3 or 4 hours at best. He asked me to run a simple test on the latest MacBook Pro just to confirm his findings: play a DVD under OS X then Windows Vista and see how battery life is impacted by the OS change.

Now I'd already ran this test on the MacBook Air earlier this year, but I had assumed that there was something wrong with my data. Repeating the DVD test (this time using an actual DVD of Sin City in the drive) I measured battery life for looping the entire movie (minus credits) on the new MacBook Pro:

Under OS X the new MacBook Pro lasted just over 3 hours while playing the DVD, but under Windows Vista I got a total of 1.5 hours. All of the bootcamp drivers were installed and the OS was as clean as could be with no additional background tasks other than what loads by default with a standard Vista Ultimate 32-bit install.

Now it's possible that Apple's notebooks may be at a battery life disadvantage under Vista vs. OS X. To find out here are the results for the Lenovo X300 compared to the MacBook Air under Vista:

The Lenovo X300 actually offers similar battery life to the MBA under Vista, despite shipping with a 27WHr battery vs. the 37WHr unit in the MacBook Air. The comparison isn't that cut and dry however; the X300 uses a Core 2 Duo L7100 with a 12W TDP compared to the 1.6/1.8GHz 20W TDP processor in the MBA. Overall platform power consumption is lower on the X300 than on the MBA and thus the numbers here seem to support my point. The X300 manages to last a bit over 2 hours during the DVD playback test under Vista, while the MacBook Air can pull nearly 4 hours under OS X (despite also staying alive for ~2 hours under Vista).

Figuring out why OS X seems to be better for battery life is nearly impossible, at least without the aid of both Apple and Microsoft. I've brought up this topic with a handful of PC OEMs in the past and they haven't been able to shed any more light on things, other than to confirm that Vista is a strange beast. It's quite possible that Vista's constant performance optimizations are preventing CPU and platform power management techniques from being effective, but that seems a little too simplistic of a view.

All I can do for now is report the numbers as is. An unexpected benefit of OS X appears to be better battery life. Go figure.