When I had my Fitbit continuously syncing all day, I noticed the battery discharging after only a few days. By disabling “All-Day Sync” within the Fitbit app, my Fitbit would last much longer by not syncing all the time unnecessarily but if I forgot to open the Fitbit app after several days to sync, I wouldn’t get the low-battery notification.
This simple app will launch the Fitbit app to sync your Fitbit device to your phone at configurable intervals (hourly, every 4 or 8 hours, once a day, or once a week).
Just install this app and in the Fitbit app disable All-Day Sync (Fitbit -> Devices -> Select your device -> Disable All-Day Sync).
On some devices such as Samsung devices, you may need remove the app from being "Optimized" for battery as the OS will kill the app process.