"Steve" wrote
Until I started adding water, I didn't realize how much they were down. More
volume below the fill neck indicator slots than I imagined.

As long as the plates remain immersed, including when the boat is
heeled (for days on one tack) if batteries are oriented fore and aft,
the only damage low water levels cause is a result of the slight
increase in concentration of the sulfuric acid; and that is minor.

I peek at the electrolyte levels every few weeks (easy access) and
fill when they are halfway down from the slots. About a liter per 12v
T105 bank.