My experience with Apple's battery replacement is also quite bad. I did the replacement for my 6s end of last November. Now I'm getting barely above 2h SOT (around 2:30). Back in the days, I used to get around 3:30 to 4:10 with IOS 11. Unfortunately I didn't measure much when the battery was new, but let's see whether the fact that it's original is worth anything. After 3 months, you're basically out of luck, and they tell you that your battery is fine anyway.