Hi there @YR-Lim, its nice to have you here in the Fitbit Community. Make sure the Heart Rate sensor of your tracker is not set On instead of Auto. You can find this option on your Android App > Tap on top of your tracker in the right upper corner > scroll down to the general section and search the Heart Rate option. When this option is configured in Auto, the green light only turns on when your tracker detects movement.
The battery drain might be related to this too, so I would recommend to try a restart on your tracker. If the option Auto of your Heart Rate is enable.
If this is not working please set up your tracker as a new devices. For additional help to set your tracker again take a look at this post.
Hope this helps. if the issue persists keep me posted.
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