The third-generation iPhone SE has some nice improvements, including support for sub- 6 GHz 5G and an A15 processor. The fact that the phone has a physically larger battery is one of the reasons Apple claims it has longer battery life.
We will have to wait for the teardowns to see how much juice Apple has. Apple is promising some decent improvements when compared to the old tech page.
Up to 50 hours of audio and up to 15 hours of video will be available for the third-generation SE. The old SE could play up to 13 hours of video, up to eight hours of streaming video, and up to 40 hours of audio.
Apple saw good battery gains by putting bigger batteries in the iPhone 13 lineup, so it's not too much of a surprise to see the company repeat that decision with the new SE. You will still get better battery life from buying one of the 13 models.
The weakest battery of the bunch, the Mini, can play up to 17 hours of video, 13 hours of streaming video, and 55 hours of audio. Even though the SE has the same chip, it doesn't support battery-hungry 5G and is physically larger. The second-gen iPhone SE was kept the same exact dimensions as the third. If it had decided to make the phone even thicker, it would have been able to improve the battery even more.