Peter Bennett wrote in
news.com:

I expect that the "shorted" cell was really a low resistance, rather
than a zero-ohm short.


It wasn't a shorted cell. It was a "dead cell". That cell had converted
lead and acid into lead sulphate crystals, so had a low gravity situation,
causing the ongoing charging problem because its voltage wouldn't come up.
These cells have quite low resistance, that's true. Lead sulphate is a
good conductor dissolved in water. What's missing is the acid. The other
cells simply forced current through the bad cell, attempting to charge it
backwards in the process, as you used it. It won't explode.

A normal battery cell that develops a short, where the plates actually
touch, is different from a dead cell. A thousand amps boils the
electrolyte as the acid-lead chemical reaction goes crazy. Acid steam
results and blows the cell, and the case, apart. Other cells may become
shorted from the impending distortion of the shorted cell pressing them
from the middle of the battery case. It isn't pretty....but it's quick!

--
Larry