Users running Windows on Apple Inc.'s Intel-based MacBook laptops have long complained about how quickly they find themselves running on empty.
"Whenever I am using Fusion [with XP] my battery life is substantially cut," wrote one typical MacBook owner last fall on the support forum for VMware Inc.'s virtualization software. "On a max charge, I am lucky if I can get an hour and 45 minutes compared to about roughly 4 hours without using Fusion."
That's not surprising. Virtualization software performs the extremely CPU-taxing task of simulating an entire PC environment to get Windows to run. This generates heat that must be dissipated by the MacBook's fan, which drains the battery even faster.
Former PC World VP and editor-in-chief Harry McCracken writes at his Technologizer site that the accelerated battery drain is the inevitable "stiff tax" of virtualization software such as VMware Fusion, Parallels Desktop and OpenOSX's WinTel.
But the vampire-like draining also afflicts users running Windows on Macs without virtualization, using Apple's Boot Camp software.
In June, popular hobbyist blog AnandTech published the results of its tests, which found that battery life for a MacBook running Vista under Boot Camp was between 25% and 50% shorter than under Mac OS X.
In a CNET review earlier this week, the reviewer found that running Windows 7 on a MacBook shortened battery life from 5 hours under Mac OS X to just 90 minutes, a reduction of more than two-thirds.
So many questions, so few answers
So, what's behind the poor battery life? Anand Lal Shimpi, AnandTech's founder and the article's author, said he couldn't say, especially since he hadn't yet tested Vista versus Mac OS X on PC hardware. The only conclusion he would draw, he said in an e-mail, is that "Apple continues to offer better battery life in general."
Others are quicker to assign fault. "If I had to guess, I'd blame Apple," said Brian Madden, a desktop virtualization analyst. "They're the ones who make the Windows 7 drivers that are used when you run Windows natively."
Jim McGregor, an analyst with In-Stat, agrees. "I would find it hard to believe that it is due to the OS, or Windows' bloat," he said. "It is likely due to the configuration with the virtualization [and/or] the drivers."
Apple did not return a request for comment. It last updated its Boot Camp drivers in April 2008.
A spokesman for Nvidia Inc., which makes the MacBook's 9400M graphic chip that controls the screen, one of the biggest energy users inside any notebook, deferred all questions to Apple.
Isidor Buchmann, president of battery equipment vendor Cadex Electronics Inc., and blogger at BatteryUniversity.com, said he thinks that Windows could be at fault.
"Think of how long it takes for Windows to boot," Buchmann said. "I compare it to the original Ford Model T, which took five minutes for you to crankstart in the morning."
Microsoft declined to comment, only saying by e-mail, "This isn't a support scenario for Microsoft (Apple is not a licensed Windows OEM) so we have no information to share."
A VMware spokeswoman noted that a June update to Fusion 2.0 "lowered overall CPU usage, which lowers overhead and helps improve battery life for all operating systems."
OpenOSX claims that battery life under its virtualization software is actually pretty good. That, says OpenOSX owner Jeshua Lacock, is due to the WinTel software being able to take advantage of the MacBook's power management features.
Will Windows 7 fare better?
According to Microsoft, Windows 7 has been re-engineered to have faster boot times and drain 11% less power than Vista.
But without new drivers from Apple or updated support from virtualization vendors, Windows 7's battery life may be as poor or worse than its predecessors.
When new drivers or support will arrive is unclear. Apple hasn't said when it will release Windows 7 drivers for Boot Camp.
VMware also declined to say when it would release new Windows 7 drivers, and otherwise officially support the OS, which is due in late October.
"We haven't done specific testing with regards to battery life and Windows 7 at this time," the WMware spokeswoman said.
That could mean many more months or years of poor battery life for Windows 7 users on MacBooks.