Apple denied this rumor, claiming the actual battery life of its iPhone 6 series defies varies within just 2-3 percent of each other. Consumer Reports decided to investigate the "chipgate" problem and found there's no significant different in battery life or temperature.
The site did a number of tests and found the performance difference of the TSMC-made and Samsung-made SoC was less than 1 to 2 percent, depending on the test:
Bottom line: Smartphones are as complicated as the people who use them, so it’s impossible to say with certainty that the battery- and temperature-performance differences we measured in this chipgate testing will be consistent in every imaginable scenario. But if iPhone 6s users are ever disappointed with their phones, we’re confident it won’t be because they bought the model with the “wrong” chip.