Here's the battery tray after a day of letting the fluid continuously circulate over the area:
Underneath where the fluid ran by, you can see how it dissolved the rust there too.
I then relocated the shower head to spray the underside for another day.
It really is neat to see how it just washes away the rust and doesn't alter the metal underneath.
Now you can really see the horrible, original welds done on these cars. It looked like the factory had some beginner junior high school students in shop class weld up the frames. I'd give them a C- for the final grade.