Sounds like your battery died. Since Fitbit in their infinite wisdom made the battery non--replaceable, your going to have to throw the whole device away and buy a brand new one.
That's why everyone like cell phone/fitness tracker/smartwatch manufacturers are putting non--replaceable batteries in their devices now....... they found if they put a lower quality battery that only lasts 2 years in their devices, they sell alot more of them than letting you replace the battery and keep the device twice as long or longer 😮 😉
