The iPhone SE has a bigger battery than the iPhone 5s

As it turns out, despite it essentially being an iPhone 6s trapped in an iPhone 5s body, it adopts the cell of neither. Instead, as a teardown courtesy of ETSupply reveals, Apple went middle of the road—a slightly larger unit than the iPhone 5s', but still smaller than the iPhone 6s'. This allows us to fill in the final piece—specs wise—of our battery table that we published on the day of the SE's announcement:
Apple iPhone SE | Apple iPhone 6s | Apple iPhone 5s | |
Audio* | 50 | 50 | 40 |
Video* | 13 | 11 | 10 |
Wi-Fi browsing* | 13 | 11 | 10 |
LTE browsing* | 13 | 10 | 10 |
3G browsing* | 12 | 10 | 8 |
3G talk* | 14 | 14 | 10 |
Battery capacity | 1624 mAh | 1715 mAh | 1560 mAh |
As you can see, on paper, the iPhone SE appears certain to deliver better battery life than even the iPhone 6s. This is due to a combination of factors, such as a smaller screen real estate and more efficient components compared to the iPhone 5s.
source: ETSupply