Since I do mostly development nowadays, and little photo/movie-editing or other CPU intensive tasks, I'm looking for laptops with large battery times. The Macb

Since I do mostly development nowadays, and little photo/movie-editing or other CPU intensive tasks, I'm looking for laptops with large battery times. The Macbook Air (battery: 7 hours?) is a decent contender. However, whenever I look at Lenovo or Dell laptops, they don't state how long the battery lasts, but instead state how big their battery is in kWh. I'm not sure but, while that may be more precise, it doesn't give me an overall clue to how many hours I should get out of the laptop on reasonably normal use.