My iPad is turning off.

When I open a app it turns off like it ran out of battery and it was below 10% but wasn't at 1 yet. It keeps doing it and it getting me mad. Do I need it to be full charge? I was just playing a game at 8% until it died or it shut off. I charge it and it turning on with apple logo like usual. Then when I unplug it to see if it happen again and it did I leave it alone for rest of the night for now. Right now am making this question. I need help is it glitched? Or normal? It had never happen for past 3 years until now. Am worried because I had it for a long time and I have important stuff in there.