The culprit here is apparently the new A9 processor, which is sourced from two different companies. Some users are seeing benchmark battery life almost 2 hours shorter, as well as a small performance different. So which CPU does your 6s have, and are you affected?
The chip manufacturers in question are TSMC and Samsung, with the latter’s CPUs allegedly chewing through battery a whole lot faster. Of course the sample size so far is small and it's hard to know if other factors are causing the issue. Either way, it's worth investigating.
The tests first came to light from a Chinese website testing the phones. Reddit user raydizzle’s GeekBench battery tests confirmed it, using two otherwise identical iPhone 6s Pluses that happened to have the two different CPUs.
Running the test over and over for consistency saw the TSMC CPU clock in at almost 8 hours, while the Samsung ran out of juice a bit over 6 hours in. The Samsung also ran hotter, and is supposedly a tiny bit slower.
Other users have confirmed similar results, but it’s not yet known if it is a widespread problem or exactly how it might change the battery life in real world use. Still, 20% is a massive difference and there are going to be a lot of unhappy customers out there if the problem is widespread.
It’s actually an odd result too, as the 14nm Samsung Chip was actually expected to be better than the 16nm TSMC CPU.
The statistics collected so far suggest that there is a 50/50 chance of each CPU across both of the new iPhones, but the 6s plus model is more affected.
The stats are about 60/40 Samsung / TSMC for the 6s Plus and 30/70 for the 6s. In other words, 6s Plus users are much more likely to be effected.
There is a few tools available to help you check which CPU you have.
The best option is Lirum Device Info Lite - System Monitor, from the app store. The CPU type can be found on the main page under model.
N71AP for the 6s and N66AP for 6s Plus are Samsung CPUs N71MAP for the 6s and N66MAP for 6s Plus are TSMC CPUs
There is also an unsigned program from a developer called Hiraku Jira that can check your CPU, but it is best avoided unless you are willing to accept the risks. Check out the website though for the CPU stats collected.
Hopefully the issue (if it exists beyond the tests so far) can be sorted by a software update.
Some users have also reported that despite having the Samsung CPU, they get good battery life in real world use. Of course that is hard to qualify, but unless you struggle to make it through a day, there is probably nothing to worry about just yet.
What CPU do you have? Tell us in the comments.