You are right it does say "maintenance free" on it. However it is not really correct. To be maintenance free, a battery must be sealed, and have some means of regenerating water from the fumes of the cells. This is not the case for the OEM Hitachi batteries. But the period until maintenance becomes necessary for adding water is unusually long, so most folks can easily get away with disregarding water level. See battery size versus capacity, and the large distance between max and min marks.