Phone shuts off unpredictably

Hello, I have an iphone 7 with an IOS 14.1

Lately, I've been encountering unexpected battery issues. at first, I noticed the battery shuts off unexpectedly at 18% then after a few days, it starts shutting off at 23%, then 28% and now it shuts off at 33%. it's as though the the phone is not telling the exact battery percentage.

What Can I Do To Fix It?