I've been having the same issues on mine, but it started in 10.0.2 about 6 days ago. I have an iPhone SE and battery life used to be amazing. I think mine might have something to do with faulty logic board or something (perhaps from a drop) because now my battery will drop 1% (say from 100% to 99%) and then drop to 98% quicker than it use to before. For example, let's say my battery drops to 99% and then I make a 30 second phone call. The phone will be down to 98%, and then if I use Safari for like 1 min it'll drop to 97 and then (sometimes) down to 96% within like 30 seconds.
I've tried hard resetting, running as a new phone without backup, signing out of iCloud, battery saver mode, etc. This SE still has warranty and I had it tested at the Apple store and they said the health was good. I also downloaded battery health apps that said the same thing, so I think it might be a hardware issue with the logic board and battery. I dropped the phone before in my house, but there are no signs of damage or anything from the outside so maybe it took shock on the inside?