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I have not used any beta release (always stable ones), but since upgrading to miui 11 I noticed an increase in battery life. I do not use my phone for gaming though, and it is whatsapp and other apps that wake the phone the ones consuming more resources.
Since the upgrade I've got about 25% increase in battery life, but as I've said, with ligth use of the phone. Mainly web browse, some media playing and whatsapp.