Check the water level frequently, especially before charging. If the level is low, add sufficient distilled water to cover the plates. After charging bring the water level up, if necessary, no higher than the bottom of the vent walls. DO NOT OVERFILL. Distilled water is best for long life, but if unavailable, it is better to use good drinking water than nothing at all. Remember..... if a portion of the plate gets dry, it loses much, if not all, of its capacity.
Follow the suggested charging guidelines.