It was discovered that Apple’s new MacBook and MacBook Pro takes a huge hit in performance when users remove battery running the notebooks off AC power.

While Gearlog’s Zach Honig benchmarked a 2.53 GHz MacBook Pro using a multiprocessor test called Cinebench R10 with third-party RAM, he noticed an usual 37% plunge in processing power. It turned out RAM was not the cause but the battery he had removed before. Re-benchmarking, the MacBook Pro showed a score of 5,549 with battery, yet it scored 3,504 only without the battery present.

Apple acknowledges the issue and explains why:

If the battery is removed from a MacBook or MacBook Pro, the computer will automatically reduce the processor speed. This prevents the computer from shutting down if it demands more power than the A/C adaptor alone can provide.

Of course, most people keep their batteries in their MacBook so this may not be a big issue. However, some like to remove their batteries and run off the AC in order to extend the battery’s life cycle and some other have not been able to replace their dead battery yet. They would not be happy with nearly 40% performance penalty, right?