Apple has released MacBook SMC Update 1.3 for the latest white polycarbonate MacBooks.
Polycarbonate MacBook computers released in early 2009 may display slower performance when started up using battery power only. Restarting using battery power may not clear the condition.
You can resolve this issue by downloading and applying this update.
Apple quietly updated the entry-level white MacBook in January to the nVidia platform that was first introduced on the unibody MacBooks.
The update is available via Software Update or via Apple's website.