I noticed that the battery level suddenly plummeted from 80% down to 40% after updating to version 3.13. I have since gone back to version 3.12 to see if the problem has been solved. WARNING - this is not an officially recognised thing to do, but it has worked for me in the past. I did a search on Google for "android fitbit old versions" and downloaded the 3.12 file. I uninstalled the current version and then installed 3.12 by clicking on the file. I logged back in and everything was running fine. You just need to disable the auto update function in Playstore. That was three days ago and I am monitoring how things go.
