I'm configuring a new MacBook Pro 15″ 2015 and wanted to know if the processor speed affects the battery life?
- 2.5GHz Quad-core Intel Core i7, Turbo Boost up to 3.7GHz
- 2.8GHz Quad-core Intel Core i7, Turbo Boost up to 4.0GHz
You want to know the 'performance per watt'. In computing, performance per watt is a measure of the energy efficiency of a particular computer architecture or computer hardware. Literally, it measures the rate of computation that can be delivered by a computer for every watt of power consumed.
2.5GHz Quad-core Intel Core i7 = 21.05 pt/W
2.8GHz Quad-core Intel Core i7 = 33.4 pt/W
So, when only looking at the 'performance per watt' you would be better of with the 2.8GHz
note: not 100% sure if I picked the correct processor types.
Considering two CPUs of the same generation (i.e. same die manufacturing process), I would expect the higher clock rate to induce some -perhaps small- increase in power consumption, as noted by CousinCocaine. This need not affect battery life directly, however:
Basically, what it boils down to is that modern laptops have huge batteries occupying a large proportion of the case. This results in longer battery charge duration, but reduces airflow.
Now, I do not have any actual numbers on battery life in similar laptops with different CPUs, so other factors may also be as important.