Haiti "Optima Eau pour Batterie"

In general, only distilled water or de-ionized filtered water is used to refill lead acid batteries.

The electrolyte consists of sulfuric acid and (distilled) water. It is only the water that (generally) leaves the battery (both at hydrogen oxygen gasses, and some evaporation. So, only water needs to be resupplied over time (some batteries use more, some use less), and others have catalysts to recombine H2+O2 gasses (palladium or similar) and/or a "filter" to separate the "mist" into liquid (drain back into battery) and gasses (vent).

On the chance that liquid electrolyte is lost (i.e., spilled or overfilled battery), refiling with a a standard strength electorolyte could be used (I guess)--But it is something usually avoided.

There are some battery additives that claim to improve/fix/slow aging of Lead Acid batteries (or even mineral oil floated on electrolyte to reduce misting/evaporation of water), but usually are avoided as not always good for batteries and sometimes make batteries difficult to recycle (i.e., cadmium additive).

https://duckduckgo.com/?q=lead+acid+battery+additives&atb=v122-1__&ia=web

The Optima liquid is probably just distilled water--But not tested/packaged for human consumption (not made sterile, etc.). I would not want to "dose" batteries with more "battery additives" every fill--Even if the aditives work, would not be very good dosing (too little at first, too much at end).

VRLA (valve regulated lead acid) and other "sealed" lead acid batteries--You can add distilled water to flooded cell. AGM and GEL type sealed batteries, not so easy to "rehydrate" correctly. (AGM are "starved" electrolyte in glass matts, GEL have electrolyte + some sort of silica product to make a stable electrolyte GEL).

You can buy catalyst caps for some batteries (not cheap, sometimes hard to find/out of stock, and do have limited life as the catalyst eventually fails):

https://www.r-charge.net/Lead-Acid-Battery-Cap-Hydro-Caps-For-T105-and-L-16_p_134.html

And there are the "filter" type (glass or plastic beads to condense liquid from mist):

https://www.solar-electric.com/batwatmiscap.html (there are different sizes available--I think--NAWS only has one size on their website--I do not work for NAWS, so that is about all I know)

Your question about adding water to VRLA/Sealed batteries that are "dry"... You don't want to let the plates to ever be exposed to air--They quickly corrode and will eventually fail.

Always refill (with distilled water) before the plates are exposed... And avoid filling a cool battery to the very top. When the batteries are charge, they get warm/hot (electrolyte expands) and they gas (gas bubbles take volume)--Both can easily cause electrolyte to go out the top of the battery (making a mess, and the question of to refill with water, or an ~1.265 specific gravity pre-mixed electrolyte).

-Bill