Gearlog has discovered a weird issue with the latest generation (Late 2008) MacBook Pros – they run like dogs when the battery is removed. To the tune of a 37-percent drop in speed without the battery.
Zach Honig benchmarked a 2.53GHz MacBook Pro with Maxon's Cinebench R10. With a battery the MacBook Pro scored 5,549, without 3,504.
An Apple support article (HT2332) claims that the performance drop in both the MacBook and MacBook Pro "prevents the computer from shutting down if it demands more power than the A/C adaptor alone can provide." It also warns again using the notebooks without the adaptor connected because "accidentally bumping the A/C adaptor could disconnect power and shutdown the computer."
Why would anyone want to use a MacBook without the battery, anyway?(Tip: Chuck Freedman, Wired Gadget Lab)