I’m experiencing the same issue since couple of months back. I had 100% battery health almost 7 months since the purchase. After that, about three months now, the battery health has degraded to 96%. Not a gamer though and I don’t even use the phone intensely. Every iOS updates also contribute to its degradation as far as I noticed. Checked the analytics of battery cycle count, the integer was 250 until 14th September. If this ratio continues, I won’t be meeting the 3 year timeline to replace the battery as Apple recommends. Can anyone help explain? Not done a factory reset even once after the purchase, should I now?