Maintenance free is a marketing gimick. As pointed out the only maintenance free are the gel cells. Distilled water is the fluid for top ups. I worked at an automotive battery shop a number of years back , we would even top up batteries without removable caps(AC Delco) by drilling the case and resealing it. Another battery scam is for dealers to replace a battery when it is drained. They will tell you they charged it and it did not respond, don't buy this story unless it has been charged for min 12-24 hours at a relativley low charging rate. From working in this field I would estimate that half of all automotive batteries replaced are in fact still servicable. Average battery life is 5years. merry hoho