Not sure if this a ploy by Apple to get folks to upgrade their older phones, but I have the exact symptoms. Phone starts out at 100% charged. Works fine and around the 40 ~ 70 % charge range it will drop to < 10% in a couple of minutes. It will charge back up to over 50% in several minutes when plugged back in.
Started a v 14.3 and is exactly the same at 14.4 Phone is an 7 plus model. Never had a issue with iPhones until now.
WillardE
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