Hello lg0409,
Thank you for using Apple Support Communities! I understand that after you started using Microsoft Teams, your MacBook Air is powering off faster than expected unless it's connected to a charger. You've come to the right place for help.
I'd like to start by seeing if we can further isolate some potential causes of this behavior. When the Mac powers off, what does your battery charge percentage show? What is the current condition of your battery?
Monitor your portable Mac computer’s battery - Apple Support
If your Mac battery runs out of charge quickly - Apple Support
CPU activity could also affect the performance and battery runtime on your Mac. The next time you use your Mac when it's not connected to the charger, and before it powers off, see if there are any specific processes utilizing a high percentage of CPU:
How to use Activity Monitor on your Mac - Apple Support
Let us know what you find and we'll go from there.
Cheers!