My iPhone is not turning on

I was travelling interstate a week ago, and my iPhone 7 plus ran out of battery and then I got to the place which I was staying at for the night, my phone was charging but when I woke up it was only 58%. I thought it could've been a faulty charger so didn't take any notice. Then started driving again and my phone again ran out of battery again so I didn't really bother putting it on charge while I was in the car. I then got to my destination and straight away I went to put it on charger. Nothing showed on the phone, I tired doing a reset by holding the power and bottom volume button but nothing seemed to be coming up. I left it to charge over night to see what would happen but when I woke up I tried turning it on but still nothing. does anyone have any suggestions on what to do or what might be causing it?