Conventional lead acid batteries , which have liquid electrolyte and removable filler plugs to allow for the periodic “topping off” of the battery electrolyte with distilled water. The Conventional battery has “fill lines” and the electrolyte levels are visible through the translucent battery case.

VRLA MF batteries  , which refer to Valve Regulated Lead Acid , Maintenance-Free. batteries ,are permanently sealed and never require the addition of distilled water.