I used to do the same same ;) Though no longer a mac user, I am also interested in this.

According to the project they've "optimized the scheduling and power consumption of the DSP processing, so you’ll get excellent battery life while playing back audio."  

Based on the info in the link below from earlier this year (Asahi Mix 39) it does seem they are continuing to improve on battery life.

https://www.notebookcheck.net/Asahi-Linux-improves-battery-life-and-graphics-features-on-Apple-Silicon-Macs.793258.0.html