That's supposed to be OK, of course, because despite any battery differences the battery-life rating of the new phone is the same as the predecessor. Also, you're getting the more powerful, faster A9 chip, which makes the iPhone 6S zippier with improved graphics performance while being energy efficient. You're getting an engineering marvel, so there shouldn't be anything to complain about.
But I'm in the camp that the cries for today's phones to get a little thicker in exchange for improved battery life, particularly as Apple promotes using your iPhone in ways that are battery-intensive (video streaming, gaming, and excessive camera use). It's also worth mentioning that having an Apple Watch tethered to your phone all day can't have a positive impact on your iPhone's battery life.
Apple takes wraps off iPhone 6S and iPhone 6S Plus (pictures)
OK, but compared to the iPhone 6S, the iPhone 6S Plus is heavier and more cumbersome and Apple doesn't seem to be calling that model less "compelling." It also doesn't seem to ever talk about how many people are walking around with battery cases like Mophies on their phones (cases which prove that almost all smartphones sold today have the same two flaws).
Apple isn't alone shrinking its battery sizes. Samsung's 2015 Galaxy and Note phones all have slightly smaller batteries, too. (The results are mixed: the Galaxy S6 fared worse than the Galaxy S5 in CNET's battery tests, but the Note 5 nicely outdistanced the Note 4 .) What's clear is that Apple and many competing companies have decided that the typical high-end smartphone is supposed to have enough battery life to get you through a full day -- at least with moderate use.
The only problem is that over time a lot of people find their phones want to take a siesta by mid-afternoon. Which is why people go out and buy battery cases. That's fine, except for those of us who remember the pre-smartphone days of those tiny analog flip phones. True, they didn't do much more than make phone calls or handle text messages (on a T9 numeric keypad to boot). But, you could go several days without recharging.
It's true that battery life can be reduced by the way you operate your phone. There are apps you can turn off, settings to tweak and tricks you can learn to run it more efficiently. Indeed, iOS 9 (the new operating system which will be available September 16 for recent iPhones, iPod Touch models and iPads) is promising battery-life improvements, including a new low-power mode.
At the end of the day, even though Apple's Ive is publicly pooh-poohing any battery-life issues, I suspect Apple's engineers are hard at work coming up with a solution that will allow Apple to make the iPhone even thinner (iPod Touch thin?) while maintaining the same battery life or perhaps even improving it. It's a challenge, though: Battery technology is notoriously hard to extend.
But there are always possibilities. A couple of months ago, Apple filed a patent for a potential solar-power charging technology. According to Patently Apple, the patent applies to "a new Apple invention that could use solar cells integrated into trackpads, the Magic Mouse, Magic Trackpad, Apple's wireless keyboard and into parts of the iPhone that could provide added stored power."
Could solar charging come to the iPhone 7? That seems a little premature, but who knows -- maybe iPhone 7S.
In the meantime, we're looking forward to testing the new iPhones to see how the battery persists in the real world.