My MacBook Air M1 battery has been draining fast after macOS 26 update

There are many facors beside OS updates the can reduce battery runtime. Diagnosing such issues in a setting like this is hard without details. But there is a secure way to generate a sterilized report that will help us.

If you want a data-driven evaluation in this setting where we can neither see nor touch your computer, please post an EtreCheck report. We can quickly and within the limitations of these forums help you determine what issues are at play without our playing a protracted game of "20 Questions" with you that could go on for days. 

EtreCheck Pro is available here: https://etrecheck.com/index

The free version will do nicely for this purpose, although the app is worthy of our financial support.

We can see hard data about resource demands, drive performance, software issues and interferences, and RAM usage. Etrecheck is the development of a long-serving and trusted ASC contributor. It is a reporting app, not a "fix-it” app, expressly for displaying information in these forums to help us help you remotely. It will not reveal any personal or secure information.

Please see this excellent user tip on how to post long text reports like EtreCheck's into a forum response:

How to use the Add Text Feature When Post… - Apple Community

Please post the entire report. What seems insignificant to a new Etrecheck user can speak volumes to those of us who have reviewed thousands of its reports. 

One thing to try: have a look at the Activity Monitor app in your Utilities folder. Sort by CPU usage and see if anything is consistently using a lot of CPU.