"SLA means "SEALED lead-acid". Is there something about the word
"sealed" that I'm missing? "

No, I was thinking maybe ddrill a hole, suck some electrolyte out and disolve some in to rejuve it. Sorta like refilling an inkjet cartridge.

Some people used to say if I had any brains I would be dangerous, but hey, maybe I can do without !

Epsom salt, that has magnesium in it right ? That's the metal that burns. Not as good as pure sodium, but burns...

That article you linked to mentions deionized water. Recently my sister bought my Mother a clock that runs on water. You have to change the water from time to time and the manual mentions something about cleaning the electrodes every once in a while.

Maybe this thing has a secondary purpose as a water deionizer ? Other than batteries and certain chemical experiments, what else might they use deionized water for ?

Hmmm.