On Saturday I started having a problem with my iPhone 8. I was attempting to take a photograph when it turned itself off. I turned it back on and found it had just 10% battery charge. Initially I thought I had forgotten to charge it, but I was sure I had. It then turned itself off again. It wouldn’t switch back on, so as I was out, I left it to deal with later.
At home I connected it to the charger and switched it back on. The charge was 100% so I disconnected it from the charger. It then turned itself off (as before). I turned it back on again and it then showed a charge of 10%. Bizarre behaviour.
I then did a reset of all the settings.
The iPhone then behaved as though I had applied a system update. It restarted itself and looked anew.
I did think maybe an aborted system update had caused the problems.
However today the same issue with the iPhone randomly turning itself off. So not sure what to do next. I think I might have to undertake a full reset of the phone.