It’s a fair question. The battery is on the border of needing to be replaced, which is a $79 repair and would probably buy me another three years or so. But at this point I want something a bit snappier and I’ll probably replace the battery and use it as a backup phone.
Not a fix for the battery, but if you're on Android, enable developer settings and change your animations to 0.5x speed (there are three settings to change). Every OS animation will take half as long. It makes an aging phone feel much snappier.