iPhone never shows battery flat symbol

Bit of a weird issue, I’ve tried “recalibrating” the battery twice by powering it on until it was completely dead and then charged right to the top.

The issue is when it hits 1% and it dies, I’m able to just power the phone back up again and no matter how low the battery gets i’m able to keep powering it on even to the point where it dies mid-boot.

Any ideas on what might be wrong with the phone/battery and what could cause this issue?

The battery health is at 91% and does last a long time, just wont show the red battery logo when its “flat”