I'm considering battery life when I'm doing general tasks
jaguarskx is right; all modern CPUs can run in a low power state.
A couple things to consider: What capacity is the battery? It's not the same for all laptops. (it's one way MFGRs can save cost)
Usually written as 4400 mAH or 47 WHr. Higher capacity is better.
Power saving mode. You'll save more power by turning down screen brightness and turning off WiFi/Bluetooth radios when not in use than you'll ever save with CPU adjustments.