Refurbished phone battery drops and restarts, but when turned on full?

Hey,

I bought a refurbished iPhone SE a few months ago. Since then I have had a problem. According to Apple Settings, the battery health is 92% (healthy). The phone, however, when I am using it the screen will go very dark, and then turn off. The battery before it turns of is always high. When the home button or power is pressed it says that the battery is gone. But, as soon as I plug it in it turns on, with my battery being higher than it was before it turned off??

This happens in cycles, lasting a day or two, and has only happened 3 or 4 times over the last 2 months. The battery has also been calibrated.

Any thoughts on the issue? The phone is still under warranty but If I tell them with no proof I imagine they may not believe me.

Any ideas on what it could be, or what is the fault?