Water level

One mechanic told me that the little ridge at the bottom of each cell-fill was the indicator as to where the fluid level was supposed to be. I've always used that as my "FULL" point.

The CORRECT LEVEL is that which is low enough to prevent purging at max charging and temperature. It is pre-determined by the manufacturer according to cell dimension and plate percentage fill. Start with a level 1/8" above the plates then check it again after max charge rate charging. If it did not rise a lot add a bit more water. Simple enough.

Really doesn't matter as long as its above. But why not play it safer,.. keep the level 1/8" below the slots at the top ? But be sure the batt is fully charged before you do that.