Automated Time Machine backups should be a “set it and forget it” strategy. Once enabled, macOS warns you only when something goes wrong. No alerts, and–almost always–the backups have continued apace. (macOS automatically runs verification tests on Time Machine volumes, or you can perform one manually.)
A Macworld reader started to receive this message on their laptop Mac and needed help diagnosing it:
No Backups for X Days
The most recent backup did not complete because your computer was running on battery.
Read more at Macworld.com