Battery % isn't always accurate. You can't trust it similar to auto-brightness.
I notice on my Pixel, I would charge it to 100%. After 15 minutes unplugged while on idle, it will say 99%. With my iPhone, it takes 30-40 min SOT for that 1% to drain. Some phones are slow burners above 50%-90%. Below it, and what was once 6 min per 1% drain becomes 3 min. You can't trust it.
The only time battery % will be useful is after you updated. If you didn't restore it, you wouldn't notice the drain. Happened to my G5 after update to Nougat. Every 2 min, 1% battery drain. Had to restore it and went back to normal.
Don't trust battery indicators 100%. Don't try to measure per minutes for 1% drain. It completely changes after it reaches a certain lower level percentage. Below 30%, it drains even faster. Again, iPhones are slow burners that first 1%-10%. Then gradually drains faster the lower it goes.