Fitbit app draining iPhone battery

[Stilskin]

When I go running, my iPhone battery is always at 100%. That's when I open the Fitbit app and start tracking my exercise. When I finish running, after an hour or so, my iPhone battery is at maybe 75-80%. But when I try to categorize my exercise, the battery drains to 0 and the phone shuts off. When it powers back up, the battery is at approximately what it was before. So it seems like something in the Fitbit app is causing the iPhone to act as though it has no more battery power left whenever I try to categorize the exercise. It also will sharply drain the battery when I don't categorize the exercise--just simply stopping the exercise tracking will drop the battery enough that the phone goes into low-power mode, so that I need to be near a charger whenever I stop tracking my run. What gives?

Moderator edit: Updated subject for clarity 

[SilviaFitbit]

@Stilskin Welcome to the Community. Thanks for the details mentioned. 

It's pretty weird that the Fitbit app is draining your iPhone's battery. I would like you to log out from your app and force quit it. Also, please restart your phone and after this double check that how much battery is your Fitbit draining on your phone. 

If you keep experiencing the same, please let me know the OS version of your phone. 

Keep me posted. 

[Stilskin]

Thank you for the reply!

I tried what you suggested -- logged out of the app, powered off the phone, then powered it back and and logged back in. I haven't had a chance to run, but I did try to recategorize a previous exercise, and then switch it back -- 4% battery power was drained by that. I will post again after I do my next run.

[SilviaFitbit]

@Stilskin Thanks for getting back. I appreciate the troubleshooting performed. 

I'll be around if you have any additional questions.