iPhone 6S screen went black and came back but battery drains very fast
So i changed Iphone 6s battery for brand new, original apple battery. After that it worked for few hours and screen went black while the phone was still working. 2 days later screen came back like normal but now battery drains very fast.(3 times fully charged during day without usage).
How can i fix it,as battery is new and this is all strange to me?