Phone battery stuck at different percenatges.

One day I noticed my battery percentage was at 48%, and had been there despite being charged throughout the night. I restart, 48%. Plugged in, and it quickly discharged to 0% and shut off within 6 minutes. Well, I came to iFixIt and re-calibrated the battery (by charging, letting it die and charging again) but I noticed that while charging the battery remained at 0%. I took it off, and then it died instantly, after the restart the phone had shot back up to 99%. It continues down normally, after it dies it then reports 0% as it should. Well, after a full recharge and restart the battery reported 27%, then after several hours began to tick down normally. The same happens every time, I’ll let it die, recharge, and it’ll be stuck at a random percentage. I’ve been dealing with this for a month, and tried everything from cache & factory resets to multiple battery recalibrations. Nothing has worked and I’m at the end of my rope. Please help me, thank you.