Affordable replacement battery for iPhone SE, I believe. The phone gave me a healthy 51% charge on the first boot after installation, which usually means the battery is good.

It drains linearly (according to the device's statistics center) and provides about 4 hours of usage with the screen on and 10+ hours of usage with the screen off.

A little myth-busting now:
"After every software update, the battery health decreases - Apple is ruining my phone so I can buy a new one!!!1"
The processor of the iPhone SE (1) is designed for the iPhone 6s, which is a larger phone and dissipates heat more easily due to its larger back surface area. The SE1, due to its smaller surface area, can overheat under certain conditions. That's why there are energy management and thermal throttling features in the phone's software that activate when the phone reaches a specific temperature. However, most of these features are unoptimized or inactive when the phone is updating its software.
Now, regarding the decrease in capacity after each OS update, I speculate that this happens because the battery heats up and gets cooked during the update, not because Apple reprograms the chip to age the battery. There was a small update for this particular phone, I installed it, and the battery health did not decrease at all. However, the overheating was evident.

Anyway, any future updates for the iPhone SE (1) are likely to be small and soon.