Nothing happens when the device's asleep, so there's not much you can do about that unless something is actively wreaking havoc here (check the logs, it'll be verbose on that front).
At runtime, nothing much happens in the background either. Disabling plugins you don't use is a good idea nonetheless, but it'll change nearly zilch, it's mainly in order to have a clearer Tools menu
.
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Sidebar: the battery gauge is wildly inaccurate. Judge stuff by how long it actually lasts, not by how much the gauge shifts.
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Sidebarē: If your FW is not up to date, or you're not booting via Nickel, that might be a factor. Nickel does a few bits of low-level shenanigans on startup, some of which might be power-management related on some devices.