Hi there, Siratus!
Thanks for reaching out to the Apple Support Communities! That's an excellent question you have about the battery life for the Apple Watches. We suggest checking out this link for Apple Watch - Compare Models. Specifically, check out the section for "Power". Be sure you also check out the information in the post-script at the bottom if the page as well.
"8. Apple Watch All-Day Battery Life testing was conducted by Apple in August 2020 using preproduction Apple Watch Series 6 (GPS) and Apple Watch Series 6 (GPS + Cellular), each paired with an iPhone; all devices were tested with prerelease software. Battery life varies by use, cellular coverage, configuration, and many other factors; actual results will vary. See apple.com/batteries and apple.com/watch/battery.html for more information.
9. Apple Watch All-Day Battery Life testing was conducted by Apple in August 2020 using preproduction Apple Watch SE (GPS) and Apple Watch SE (GPS + Cellular), each paired with an iPhone; all devices were tested with prerelease software. Battery life varies by use, cellular coverage, configuration, and many other factors; actual results will vary. See apple.com/batteries and apple.com/watch/battery.html for more information.
10. Apple Watch All-Day Battery Life testing was conducted by Apple in August 2018 using shipping Apple Watch Series 3 (GPS) each paired with an iPhone; all devices were tested with prerelease software. Battery life varies by use, cellular coverage, configuration, and many other factors; actual results will vary. See apple.com/batteries and apple.com/watch/battery.html for more information."
Thanks again for the question and have a super day!