Iphone restarting/battery level fluctuating

Hi, my iphone is having the problems described in the title, it is constantly restarting and the battery level is wildly fluctuating. It will be completely charged and then the next minute it will be empty and the phone is restarting itself. I am including a screenshot of the battery information in settings, it appears that the battery itself is not the problem. I'm guessing it is related to the "peak performance capability" issue mentioned below.

My ios is up to date. I've also tried resetting the network settings. Any help to solve this problem would be greatly appreciated. Thank you!