SharePoint 2016: Databases running in compatibility range, upgrade recommended

Problem

You have perform an initial core install of SharePoint 2016 onto a single server.  You have not yet created user content web applications or instantiated any service applications. Later, you check Health Reports and see the following warning:

Title	Databases running in compatibility range, upgrade recommended
Severity	2 - Warning
Category	Configuration
Explanation	The following databases have versions that are older than the current SharePoint software, but are within the backwards compatible range: [central admin content database].
Remedy	To achieve optimal results from these databases, use Upgrade-SPContentDatabase to upgrade Content databases, or psconfig.exe to upgrade other databases. For more information about this rule, see http://go.microsoft.com/fwlink/?LinkID=142697
Failing Servers
Failing Services	SPTimerService (SPTimerV4)
Rule Settings	View

Understanding this to be a content database, you open an elevated SharePoint Management Shell and execute the following commandlet: Upgrade-SPContentDatabase [central admin content database]. However, this returns an error: The content database could not be found.  This doesn't make sense. You begin troubleshooting.

Troubleshooting

1. Check database status:
1. In Central Administration, navigate to: Upgrade and Migration > Upgrade and Patch Management > Review database status.
2. Found that the Central Administration content database was listed as Database is in compatibility range and upgrade is recommended.
2. Get database instance
1. In an elevated SharePoint Management Shell, executed Get-SPContentDatabase: this returned nothing.  This indicated that the farm content database is not considered to be a content database per se, even though it is in fact storing content.
2. Execute Get-SPDatabase | ft -auto: this returns all databases: the farm content database and the farm configuration database.
3. Execute PSCONFIG
1. In an elevated SharePoint Management Shell, executed: Psconfig.exe -cmd upgrade -inplace b2b -wait -force.  Completed successfully.
2. Navigate to: Upgrade and Migration > Upgrade and Patch Management > Review database status.  Found that 

Solution

1. Execute PSCONFIG.

References

• TechNet
• Get-SPContentDatabase
• Get-SPDatabase
• Psconfig command-line reference (SharePoint Server 2010): still valid for 2013
• Upgrade content databases to SharePoint 2013
• Verify database upgrades in SharePoint 2013
• Troubleshoot database upgrade issues in SharePoint 2013