Why does my ifixit battery heat up so on charging? holds charge poorly

I installed new ifixit battery in my Iphone 6s per instructions and calibrated it as recommended. The phone works fine, but battery and charging plug heat up when charging (I’ve tried several plugs) , and the battery performs a little better than my old one, but discharges much sooner than I expected. If I am listening to Podcast, lasts about 6-8 hours