If you replace your battery, the notification is resolved. Since 1.16 it is a persitent notification and the Led bar is used tosignal the user this notification is present. The early crore have toom much standby power from the battery and therfore it gets easily drained when th ecore is not powered. I beleive you can get a replacement if this is a problem for you. If you core is powerred 24/7 it is less of a problem.
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