No. CPU's in a phone are probably idling 99% of the time. The power usage for the full-performance and half-performance cpu when idling will be close to equal.

No. CPU's in a phone are probably idling 99% of the time. The power usage for the full-performance and half-performance cpu when idling will be close to equal. The full-performance phone might even have better battery life because it can finish cpu intensive tasks twice as fast, returning to idle power draw faster than the half-performance phone.