Is it possible to Batch Rename a folder of images in Photos?

Yes, with one of these:

Batch Change Title to Text w/Padded Sequential Numbers

Batch Change the Title of selected Photos to the Description/Caption - Apple Community

Batch Change Title to Capture Date-Description-Padded Sequential Numbers

Script: Batch Change the Title of a Photo to the Filename Followed by the Existing Title

Script: Batch Change the Titles to a Given String

The scripts compiled as an applications can be downloaded from this tutorial site:  P01 - Applescripts from Photos’ User Tips Compiled as Applications  

Another option if you don't like scripts is Photos Workbench (beta 24) from Houdah Software. This is a beta version-- it is free but not finished, yet.

https://www.houdah.com/photosWorkbench/

I have used it to add index numbers to pre-existing title names, moving parts around for easy sorting, and it has worked very well. Here is an example where I put the date first as 2022 04 01, and then an index, followed by the title that I currently had on the pictures. Each of the variables can be inserted or deleted independently, as well as text (like the -- in the example), and a number of other options like file name, etc. In then shows an example of a photo title before and after the change so you can see what you've done before doing it.

It's free so far, and they keep adding stuff-- it's worth a look.

I have several Photos libraries and my only small quibble (unless I have missed the option) is that it works with the system library so I have to make the library I want to use it with the system library. It would be perfect if it asked which library I would like to use.

I have certainly let them know that very thing. Here is their response, about 5 weeks ago:

"Version 1 of Photos Workbench can only work with the system library.

We plan to change that in an update."

So I have my fingers crossed. They did provide support, in the latest update, for custom ordered albums after I requested it-- I don't know if my request was a cause, of course. You can let them know your thoughts here:

https://forums.houdah.com/photos-workbench-support-902966

Happy New Year

This can be done with an Apple script. See this document

https://discussions.apple.com/docs/DOC-250000226

which has links to different scripts that you can adapt to your purposes.

The first time you try to run the app version Control (right) - click on it and select Open from the contextual menu. Then click on Open in the next window and you'll be good to go.