Iphone 5 Is Over heating while using WIFI

I had Purchased An Iphone 5 On December 30-2015 and i gifted it to my Sister on Her Birthday.. After a couple of days while using Wifi, skype,youtube the temperature gets hot and battery is poor weak... it was 80-95 %at 11Pm and when i saw it At 7 Am it was completely Switched off.