27 months in and my S4 40mm launch day unit is at 75% health. Still lasts a day but barely (10-20% by 10pm). I had to turn off background app refresh, noise and handwashing.
3 months ago, it was at 85%. Kinda leads credence to exponential degradation small batteries Are known for (Airpods, for example).
Can’t wait for the rumored redesign coming this September.