According to a browser efficiency comparison for Windows 10 version 1809 (which Microsoft posted on GitHub but never advertised),
Edge remains the best browser for battery life: measuring the time it took identical Surface Book laptops to run fully through their batteries while streaming HTML5 video in fullscreen, Edge lasted 24% longer than Chrome and 94% longer than Firefox.
Despite the browser's adoption of Chromium, Thurrott believes Edge will retain this strength due to "underlying integration with the operating system."