I just went through this disaster with my SL Twin-Task 3C.
The middle battery was the one that yucked all over the place.
After pounding the tail on a board for awhile, the middle battery moved enough to allow the battery near the head to act as a ram of sorts, and it finally came out.
This is the first time this has happened with any of my 50 or so lights.
It was common in the lead-acid days.
This light was used by relatives on a vacation, runtime unknown (other than I knew it WAS used). Forgot to replace the batteries.
Moral: replace partially depleted batteries.
A half round ******* file was used to smooth the really rusty/corroded side. Liberal application of Breakfree CLP, and swabbing like a mad woodpecker got most of the crud out.