So... this might sound super crazy, but my launch Series 3 that was my flatmate's and then mine since a couple years ago (when he upgraded to a series 6) is still at 100% battery health and I have zero complaints about the battery life. I even sleep with it for sleep tracking and alarms because I don't have to worry about it letting me down and as long as I remember to drop it in the charger a couple hours during the day it just keeps going for a whole day or even a day and a half. I don't know if it was our use case (basically notifications and very light training tracking) combined with a conservative charging pattern (optimised charge on and, since I got it, it has never spent a whole night at the charger) but it's almost magic.
Edit: I very VERY rarely let it charge to 100% and I just pick it out of the charger as soon as it's like 70-80% ish. Then it can easily go for a day and a half.
Edit: I very VERY rarely let it charge to 100% and I just pick it out of the charger as soon as it's like 70-80% ish. Then it can easily go for a day and a half.