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.
There used to be a jailbreak app for iphone to increase animation speed, it was soooo nice, it felt like you were actually using the phone instead of the phone using you. Anything out there for iPhone right now? Edit: cowabunga on iOS 17 (broken in iOS 18+) https://cowabun.ga/