I’ve noticed a substantial improvement in the battery life of my M4 13-inch iPad Pro by disabling background app refreshes for almost all my applications. Currently, I only have three apps that are automatically refreshing in the background, and I’ve discovered that I don’t require them to constantly refresh. It appears that almost every time you install an app, it sets the app refresh by default.
I suspect that the potential for battery life improvement will depend on how frequently one switches apps. More frequent switching may minimize or even negate the gains from disabling background refresh, but in my use case, it has improved battery life.