Eric Cobb shows how you can use dbatools to upgrade multiple SQL Server instances:
Patching SQL Server can sometimes be a time consuming process, especially when you have multiple servers that need to be patched. Remoting in to each box to run through the update wizard is tedious, and if you have multiple patches to apply you’re going to be spending a considerable chunk of time on it.
Thankfully, the dbatool Powershell Module makes this process much easier! In fact, once you get it figured out, using Update-DbaInstance to patch your SQL Servers becomes very simple. But, getting it figured out can be a little confusing, so I’ve outlined the steps below that I use. The biggest hangups I had were setting up a central patching location and using a credential to access it.
Click through to see an example of this in action.