Update 4/4/2024

Added button that saves all lightmaps to render directory.
Improved node placement and bug fixes.
UI replaces python console

Setup:

Download the compressed addon
Navigate to preferences and install/enable the add-on

For stability, join all objects in collection to one mesh.
Double check all materials to see that:

• That each material uses shader nodes.
• Each object has uv2 map.
  • Default "UVMap" is for texture coordinates, "uv2" is for shared light-map coordinates.
• Materials do not exist in more than collection.
  • Example: if concrete is in lightmap1 and lightmap2 collections, duplicate it so there is concrete and concrete.001

Name collections; Add _lightmap2048 suffix/flag to collections that belong together

• "level2_lightmap512" will bake to an image called level2_512 (at 512px^2 resolution)
• "scene5_lightmap2048" will bake to an image called scene5_2048 (at 2048px^2 resolution)

Run:

Based on what type of bake you want, hit either the "Complete" or "Bounce" button.
Then hit the bake button to start a cycles render job

After the bake completes, you should be able to find them in the image viewer.
Quickly and easily write every lightmap to disk with a single mouseclick, by pressing the "Save Lightmaps" button

How it works:
Utility creates 1 image per collection.
Modifies all materials
All materials write to a collection light-map.
Adjust Samples / Denoising with standard cycles render settings.