We are continually working on improving battery life. One thing that may help in the meantime is using Dark theme, which was a top mobile request added to Teams mobile in February.
Even with backgrouns tasks turned off on my iPhone, the app remains a real battery hog. This happens even if I kill the app in the app switcher. I have the same issue on my iPad as well...
This is currently in Preview – planned to release very soon.
In the following weeks, Teams will be rolling out support on Safari 11+ on macOS. While in preview, there are known issues with Safari’s ITP mode and it is advised that users disable Safari’s Intelligent Tracking Prevention.