DxOMark has started evaluating smartphone battery life, and the Galaxy S21 Ultra has fared poorly. The Exynos 2100 version languishes near the bottom of DxOMark's battery leaderboard, but the overall score is more than just a measure of battery life.
https://www.notebookcheck.net/Samsung-Galaxy-S21-Ultra-with-an-Exynos-2100-SoC-sinks-in-DxOMark-s-new-battery.539451.0.html