I recently purchased a laptop with an i7-640m processor (blinded by a discount), and my battery life is fairly horrendous: the manufacturer given battery life is 6 hours (I know, it's an upper bound), and I barely squeeze out 3 hours with light usage+wifi. I can't seem to find any information on whether swapping out the processor for a i5 or even an i3 would significantly extend the battery life, aside from people baldly asserting "it should extend battery life" and my own intuition.
Has anyone tried to quantitatively compare these processor families with respect to battery life?
Note that the upper-bound on the battery life was probably with the default i5 configuration, and that my laptop heats up very quickly and stays hot, possibly pointing to more power dissipation than the laptop was designed to handle. I should also note that Engadget gets around 5.5 hours with a similar usage profile, for a i5 configuration. The TDP is exactly the same for all three (i3-3xxm, i5-5xxm, i7-6xxm)