The proper level for the fluid (Acid water mix) is between the top of teh plates (Meaning they should be covered) to JUST BELOW the bottom of the filler tube or split ring,, like 1/8 to 1/4 inch..
If they are down.. Fill to about the mid point, fully charge and eqaualize, then top off. to 1/8 inch below the tube.. NOTE: midpoint need not be all that accurate. Anything over the plates and say half an inch below tube is OK.
Tube used to be called "Split Ring" look down it and you will understand why.
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