Currently there is no way to take the power saving preferences into account. Having a media query to check these (if technically possible), would help creating more sustainable websites. Even if it's not technically possible yet, it might be a thing to consider for future development.

Example:

/* Battery saving mode enabled */
@media (prefers-battery-saving: high) {
  body {
      background: #000;
  }
}

/* Battery saving mode disabled */
@media (prefers-battery-saving: none) {
  body {
      background: #fff;
  }
}

The media query could be used to:

• load lower resolution images & videos or prevent loading them in general
• use darker colors for OLED screens (darker than dark mode)
• disable transitions and animations (like prefers-reduced-motion)
• toggle specific JS functions via matchMedia
• load different Fonts

I think the impact of the media query could be huge and it would be a step in the right direction for a more sustainable web.