My iPhone runs out of battery?

So I was playing an app just now, then after 20 seconds it became 100% to 0%. How do I fix this problem?

Welp.

1 What kind of iPhone

2 Has it ever done this before

3 How long have you had it

4 what game is it

5 what OS update are you on

6 what other apps are you running

7 what carrier are you on

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