Common issues which cause battery drain:

• Dual gpu are the most common cause of battery drain, the easiest way to fix it is to blacklist the dual gpu module (e.g. adding "module_blacklist=nouveau" to the kernel command line).
• IPU3 camera recovery images cause a battery drain due to the android camera service running in an endless loop in the background (ipu3 recovery images are notably nocturne, atlas, nautilus, soraka).
• The use of crostini causes battery drain: xalexis from telegram croissant group gets 1.5 hours more screen on time of a full charge with crostini disabled (but that may depend of the packages you have installed).

If you are not in the above cases, there are some basic things to consider when comparing battery life between ChromeOS and Windows/Linux:

• Do you have the same use in Windows and ChromeOS ? Clearly, you cannot compare the battery life with simple browsing in windows and playing android games in ChromeOS. Try to compare objective things like battery life when playing youtube videos in the browser or things like that.
• Do you have the same brightness setting in windows and chromeos ? Screen brightness is very high by default in ChromeOS which has a clear impact on battery drain.

Don't hesitate to discuss battery life here and to share your battery life related tips.