Shutting off at progressively higher % battery remaining

Hello,
I’ve got an ASUS C434 (Shyvana) which I put a new battery into a few months ago. All was great in that I could go a couple days without charging. I never let it drop below 10% before charging. A couple weeks ago, the device shutdown with 10% battery left. After recharging, it shutdown with 12% (or so, I don’t remember exactly). Then 15%, then 20%… Fast forward a couple weeks to last night and it shuts down with 75% remaining.

The Energy app in F41 KDE Plasma shows battery Health: 89%. So there could be a battery issue. That aside, could there be an issue with what coreboot is reporting to F41 and it keeps thinking there is perpetually only 89% of what was previously available?

A battery for this CB is about $50 and the device isn’t worth much more. So if it is a battery issue, I’ll look for a new one during Black Friday. But I’m hoping it’s something I can fix as this is a decent device with F41 on it.