Interesting. Since I have had to contact FITBIT about a sense 2 that exploded ( there was a loud pop/ sharp burn/ flash of light/ watch face shattered) on my wrist as i was sleeping.
After going through their protocols/ talking to some r& d person/ sending photos of watch and burn/  they sent me a a replacement sense 2

After updating the firmware on my 3 year old Sense, the battery life indicator stopped working. It has said 100% since last night. Typically, I normally drop from between 10 and 20% overnight. Unless they've magically find a way to have eternal battery life, they did something wrong with the firmware update.