If your phone wasn’t shutting down at 50% with the old battery but is with the new one than it could be that the battery you purchased is faulty. But first I would check that the battery connector is seated properly. There is also some components on the logic board around the battery connector that if nudged can cause problems with the battery data but this usually results in boot looping and no battery data. [link|https://help.ifixit.com/article/273-how-do-i-return-something-i-ordered|I would return the battery for a replacement one.|new_window=true]