No, the app is not doing any activities in the background. You can even close the app and it will reappear on wakeup time. Of course the wakeup by light in the morning will consume some battery. We recommend to plug in the charging cable overnight so you can leave the house with a fully charged device.
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Phone Assistant / Manager / Battery / Eco. ModeTurn off Eco Mode Phone Assistant / Manager / Battery / Optimized ModeDisable optimized mode […]
No. The night mode is optional. You can even close the app and it will reappear on wakeup time.
Device Settings / Battery / App Battery ManagementSelect Gentle Wakeup in the list and enable Allow all background activity Pin your app […]
Settings / Apps / Special App Access / Autostart or Settings / More settings / Applications / Autostart or Manager / App […]