Phone is lagging horribly below 50%

I have had this iPhone6s plus since about 2016 and replaced the battery once before because of the “battery causing lag” and now when my phone gets below 50%-60% it lags horribly, looks like 20FPS on the home screen with everything disabled. I have tried everything besides replacing the battery itself since I don’t have the money right now. It is to the point where I can’t even open some apps unless my phone is plugged in.