Phone dies at 70% with new ifixit battery

Hi yall!

So I swapped out my phones battery with an ifixit replacement about 2 weeks ago and it was working great up until a few days ago. It just shuts down at around 70% and needs to be recharged from 0%. There was one time where I put it on the charger after it died and it would read 69% but would keep dying instantly unless it reached 70% capacity.

This happens multiple times a day and my phone is useless most of the day. Is there any way to fix this? I also still have the original Samsung battery but I bent it a little bit while removing it. Is the original battery safe for usage until this gets sorted?