help stuck at 2%

I have an iphone 6s plus ios 11.2.2, today i was using my phone normally as always but suddenly i was starting to notice the battery wasnt draining and it was stuck at 52 percent with low power mode, for me i just didnt mind that bc i was thinking that it might not die early so i kept using it until my phone started lagging like crazy, so i restarted it then when it turned back on, it was only 1 percent then it went 2 percent after 4 hours it is still stuck at 2 percent. Please help me i dont know what to do, i already tried hard reseting and also changed the adaptor but i didnt reset all data yet. Please help me out