Why Did My Phone Just Randomly Shut off and How Can I Fix That?

So the other day my phone, an iPhone SE that's about a year old, powered off -- for what felt at the time like no reason at all -- and wouldn't turn back on, AND didn't even do that thing where it flashes the low battery icon when the battery is dead.

In retrospect, there were maybe some reasons for this. The battery was low, maybe 18%, it was cold out, it was snowing, and I was actually using the phone in all of this, because, you know, gotta be on the phone all the time.

Turned the phone back on. Nothing. Eff. Plugged the phone into its charger, let it sit for a few minutes, turned it back on, now it's working. Great!

Checking Battery Health on my iPhone SE Running 11.4.1

Battery

Checking battery health isn't available on the iPhone 5s. It DOES work on the iPhone 6/s/plus, SE, 7/plus, etc.

Battery health seems like a temporary fix and I kind of wish this were a more permenant feature and that it offered more control like allowing some kind of throttling to be manually turned on and off.

On my iPhone SE, which is about a year old, my maximim capacity is 94%, compared to when it was new, and there's a notice at the bottom of the screen about how there was an unexpected shutdown and performance management has been applied. I can apparently disable performance management by tapping the little blue Disable... button at the end of the notice about performance management. I'm worried that if I disable this setting it could make the phone less stable overall and that I won't be able to re-enable it unless there's another random shutdown.