When my SE1 battery was giving trouble, which started in the mid- to high-eighties percent Battery Health, the phone assured me that the condition was good enough to support normal function. Finally, with random power-offs and high drain in normal use - in other words, hopelessly incapable of supporting normal function - I replaced it myself and all the problems were fixed.

Battery life is not as good as when it was new, but I don’t know why that is. I think it’s a common experience, though. Ageing components? Running later versions? Who knows.

The fact that mine is good proves that the phone is still viable, so I’m guessing that something is wrong with yours - perhaps a bad battery.

Can you try a different charging lead? That may be the problem.

Do you mean that you bought it five months ago and immediately had the battery replaced? “Literally just bought the phone” doesn’t mean 5mo ago.

Batteries is batteries. Who knows why these things happen? But they do. I don’t check battery health any more. I’ve no idea what it is on my SE2, bought mid-2021. When the battery obviously affects performance adversely, I’ll replace it.

I just downloaded a 253mb banking app on mine and it dropped from 26% to 25%.

I’m still using my SE1, though my main phone is an SE2. The SE1 is still usable, in my opinion, and an Apple-replaced battery is still available for £65. There are also third-party batteries, some of which are trustworthy.

I intend to buy an SE3 soon but there’s no doubt that the original SE is unbeatable for pocketability and ease of one-handed use, compared to the later SE versions.

That’s one sign of a bad battery. I had it. A good replacement was the fix.