Some strangeness with the battery on my iPhone SE (original). If it's over 50% in the evening, I normally just leave it and it's good for the second day. Recently when I look at it in the morning, it's down to 1%. Today I put it on charge, then started using it when at 83%. Just noticed it's down to 1% again, put it back on charge, and it's 57% straight away!
When I found the battery level history thing, it showed it fine last night until about 1:30n am, then suddenly straight down to 1%.
Today it shows it starting at 83%, then suddenly dropping to about 40% (might have been a Facetime session in a dodgy part of the house). Stayed flat at that level, then 10% then 1% just like that. Plug it in, and immediately up over 50%!!!
EDIT: realise that about the time the battery level crashed, I was sitting in the car outside a supermarket sending a text to my wife, who was inside finishing the shopping... so it was connected to the car's systems via bluetooth...
I did close it down and reboot after plugging it in the second time...