Sense 2 battery fluctuates in past few weeks

[samuraiwil]

I've had my Sense 2 for a few months now, but I've started having an odd battery issue in the past few weeks. I generally charge my fitbit to 100% just before going to bed. Some days, when I wake in the morning, the battery will be around 94% or 95%. And then during the day, until I charge it again, it the battery will drop to maybe 70% or 75%. Same thing the next day or two.

But then there will come a day when the battery will be around 80% in the morning, and by night it will be down to 15% or 20%. (Or a couple of times, even have drained completely before my usual charging time.) That will happen for maybe 2 or 3 says, and then my fitbit will revert to the former low-battery-usage state for a couple of days. 

There's no marked difference between my activity level or the apps I use during those days, so why the wild fluctuation in battery usage from one day to the next? Does my better need replacement? (And is there even a way/place to get the battery replaced?) Any thoughts?

Moderator Edit: Clarified subject

[Guy_]

Hi @samuraiwil - it's definitely not a battery issue and they can't be replaced, only the whole watch under warranty.

It is more likely a syncing issue, which under certain circumstances can drain the battery, or even a firmware distribution in background, in which case you may notice a phone battery issue too.

To avoid this logout of the Fitbit App, clear the storage cache and force stop it. restart both phone and watch. How do I restart my Fitbit device?