The “service recommended” state of the battery aside, I would start by using the Activity Monitor to see if there’s something using a lot of power: open Finder, click Applications, open the Utilities folder, and open Activity Monitor. Click the Energy tab at the top, then click the “12-Hour Power” heading to sort by that column. That will show you a relative measure of what’s used the most power recently. Is there an entry in the list that is much higher than others?

Also, use Windows 10 LTSC. You can download an eval copy from Microsoft and turn it into the full version by following the instructions here to change the installed SKUs: https://github.com/victorlish/Convert_to_Windows_10_LTSC. Then use the KMS scripts above to activate it.

Ignore the FUD about “LTSC is designed for specialty purpose machines like medical devices, retail kiosks, blah blah blah.” It is what Windows 10 should have been: no bloatware, no ads, no MS Store (you can add it back if you want). No forced upgrades. I’ve used it as my daily driver since Windows 7 went EOL, and I’ll never use a “normal” version of Windows again.