iPhone keeps turning off and won’t turn on for a few hours, time for it to fix itself increasing.

my iPhone 11 is about 3 years old now, I’ve been content with it so far but over the past year it’s started randomly turning itself off for no reason. Just a black screen.

At first I was able to turn it on holding the down volume button and the power button but for the past few months it turns itself off at random times and won’t turn on for a few hours before turning itself on.

yesterday was the worst when I needed it and it turned itself off at the start of the day and would not turn on all day. I put it in the charger all night, even though I knew I had charge. It was not working in the morning still and only about an hour ago did it work again.

I attempted to turn in on and the no battery image showed on screen, which is the first time this has happened.

I knew it should have had charge since I charged it all last night but whatever. Does anybody know why this might be happening?