Try the same thing only leave it at 50% after you have been using it and report back what percentage you lose. I'm betting it'll be 3-7% for 8 hours standby depending on your settingsCharged at 100%, went to bed, woke up 8 hours later still at 100%. Never happened to other iOSes before.
It's pretty much always been like that. Battery percentages are estimates based on voltage and when the battery is fully charged or is almost depleted the voltage differences aren't as sensitive basically so it takes somewhat longer at each of those extremes (usually at least).I think it's a scam. I reckon the iOS team deliberately makes the battery report 100% a bit long to make us users feel like the battery level is amazing. Because once it has dropped to 99%, it's free fall to around 70% in under 2 hours on my iPhone 6.