Any function using GPS will drain the battery within a few hours. You probably won't get much more than 6+ hours on GPS from a fully charged battery. This will vary depending on the condition of the battery. Ensure nothing is using GPS. Remove the device from the Fitbit app, then unpair from your phone and THEN do a factory reset. Do this connected to a charger and ensure it IS charging before the reset.
Setup again as if it was a newly purchase device.
