A Calcium battery is a still a lead acid battery; they are usually sealed maintenance free. Calcium replaces antimony in the plates of the battery to give it some advantages including improved resistance to corrosion, no excessive gassing, less water usage and lower self discharge. Silver is another additive used by some manufacturers, the addition of silver enables the battery to be more resilient to high temperatures.
Calcium batteries require a higher charge voltage than conventional batteries. If used in a deep cycle situation it is advisable to use a charger designed for calcium batteries of has a calcium charging mode to get the maximum life out of the battery.