The iPhone SE has incredible battery life
Geoffrey Fowler from Wall Street Journal put the iPhone SE through a "stress test" that involved cycling through websites at the same brightness level. Fowler found that the SE lasted 10 hours, which is two hours longer than the iPhone 6s and 5s in the same test, and "nearly three hours longer than the Galaxy S7."
Indeed, the battery life estimates Apple listed for the iPhone SE are better than the iPhone 6s Plus, which has a much bigger battery.
So, how does the SE have such a good battery life despite having a smaller battery than most other premium smartphones?
Most of it has to do with the relatively small 4-inch screen. Your smartphone's screen is the main culprit when it comes to battery drain, as it's literally shining a powerful light through a bunch of pixels in the display. The smaller the screen, the less light it has to shine, and the less power it draws.
Much of it also has to do with the power-efficient A9 chip that's running the iPhone SE, too. The battery life comparison between the iPhone SE and the iPhone 5s is a good example.
Both have the same size screen, and yet the SE lasted two hours longer in Fowler's test because the A9 chip is more power-efficient than the 5s' A7 chip. Sure, the SE has a marginally bigger battery than the 5s, but it's not big enough to warrant a full two hours of extra battery life. If the iPhone 5s also had the A9 chip, it's entirely likely that the battery life would be similar to the iPhone SE.
Some might be underwhelmed by the fact that the SE looks nearly identical to a smartphone that was released in 2012 (the iPhone 5), but considering it has the premium specs and most of the features of the iPhone 6s on top of the great battery life - not to mention its relatively low $400 price tag - it's looking like a winner on most fronts.