Do you have a source for that? It seems like many of the times Apple upgrades their chip, they advertise greater power efficiency. E.g. for the A13 (from Wikipedia):
> Apple claims the two high performance cores are 20% faster with 30% reduction in power consumption, and the four high efficiency cores are 20% faster with a 40% reduction in power when compared to the A12.
Similarly the A12:
> It has two high-performance cores which are claimed to be 15% faster and 50% more energy-efficient than the Apple A11
And A8:
> Apple states that it has 25% more CPU performance and 50% more graphics performance while drawing only 50% of the power of its predecessor, the Apple A7.
I've searched the web and can't seem to find any source that actually specifies power consumption of Apple's chips by generation, stretching from the A6 to A13.
So for all I know, the 11's CPU with the 5's battery might be far better, not far worse. It doesn't seem like any kind of law that newer processors use more energy. So only actual data will give an answer.