Is it okay to charge iPhone to 20 percent?

My new iPhone died I charged it to 20% then it died charged it again to about the same then it died then I did the same again.

It all depends on how often you are doing this. If you do it quite frequently, you may see a decrease in the total battery life. Try to keep the phone on the charger if you can. I would also suggest buying a car charger, they come in handy!