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.
To determine if your computer is eligible for this update, see EFI and SMC firmware updates for Intel-based Mac.
For more information on SMC updates and step by step installation instructions, see About the SMC Firmware Updates.