Apple's latest iPhone has shipped with two slightly different versions of the A9 processor, one made by Samsung, and one by TSMC. Some people have reported a difference in battery life depending on the chip inside, but Apple disagrees.
According to a few side-by-side tests reported on forums and YouTube, the TSMC processor gets two more hours of battery life than Samsung's chip. But Apple's hit back at claims that the two chips give users different battery life. In a statement provided to TechCrunch, the company said:
Certain manufactured lab tests which run the processors with a continuous heavy workload until the battery depletes are not representative of real-world usage, since they spend an unrealistic amount of time at the highest CPU performance state. It's a misleading way to measure real-world battery life. Our testing and customer data show the actual battery life of the iPhone 6s and iPhone 6s Plus, even taking into account variable component differences, vary within just 2-3% of each other.
Apple is freely admitting that there are slight differences between the two processors. But it's also pointing out that the side-by-side battery tests most people are relying on aren't representative of real-world use — which, to be totally fair, they aren't.
The problem is, there's no good, objective way to measure 'real-world' battery use. Day-to-day usage is a weird mix of standby, where the bulk of the battery use is the cellular radios, and screen-on time, where the screen backlight and processor burn up most of the battery.
The Geekbench battery test was the one used to generate the claim that the TSMC chip runs for two hours longer. It's a particularly CPU-intensive battery test, so Apple definitely has a point that it would stress the CPU battery use more, thereby exaggerating any power-usage differences between the two processors.
At the same time, this shouldn't be a let-off for Apple. It's notorious for playing down very real issues with its phones, and until we get a more representative side-by-side comparison (in the works!), the jury is very much still out.