iPhone batteries are small in general. My GF's iPhone se (don't ask me which gen) barely lasted half a day, and took hours to charge. So a couple of years ago I bought her a Z Flip 3 for her birthday because all the girls in the Korean shows she watches had that phone at the time. Now her battery actually lasts a full day, and the phone charges to full in 45 minutes.
The larger iPhones easily last a day. The SE (any gen) are fairly small and thin and don’t have very large batteries. The 12 and 13 mini are also very small and thus don’t have much battery life. If you have a regular sized iPhone or even a Max, battery life is fine, on the bigger ones good even.